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Concept: Hue


The West African Gaboon viper (Bitis rhinoceros) is a master of camouflage due to its colouration pattern. Its skin is geometrically patterned and features black spots that purport an exceptional spatial depth due to their velvety surface texture. Our study shades light on micromorphology, optical characteristics and principles behind such a velvet black appearance. We revealed a unique hierarchical pattern of leaf-like microstructures striated with nanoridges on the snake scales that coincides with the distribution of black colouration. Velvet black sites demonstrate four times lower reflectance and higher absorbance than other scales in the UV - near IR spectral range. The combination of surface structures impeding reflectance and absorbing dark pigments, deposited in the skin material, provides reflecting less than 11% of the light reflected by a polytetrafluoroethylene diffuse reflectance standard in any direction. A view-angle independent black structural colour in snakes is reported here for the first time.

Concepts: Light, Color, Spectrum, Rainbow, Hue, Viperinae, Snake, Bitis gabonica


Shape plays an important role in defining the function of materials, particularly those found in nature. Several strategies exist to program materials to change from one shape to another; however, few can temporally and spatially control the shape. Programming the sequence of shape transformation with temporal control has been driven by the desire to generate complex shapes with high yield and to create multiple shapes from the same starting material. This paper demonstrates a markedly simple strategy for programmed self-folding of two-dimensional (2D) polymer sheets into 3D objects in a sequential manner using external light. Printed ink on the surface of the polymer sheets discriminately absorbs light on the basis of the wavelength of the light and the color of the ink that defines the hinge about which the sheet folds. The absorbed light gradually heats the underlying polymer across the thickness of the sheet, which causes relief of strain to induce folding. These color patterns can be designed to absorb only specific wavelengths of light (or to absorb differently at the same wavelength using color hues), thereby providing control of sheet folding with respect to time and space. This type of shape programming may have numerous applications, including reconfigurable electronics, actuators, sensors, implantable devices, smart packaging, and deployable structures.

Concepts: Fundamental physics concepts, Light, Electromagnetic radiation, Absorption, Wavelength, Digestion, Hue, Visible spectrum


Retinoblastoma is the most common primary intraocular tumor in children. The first sign that is often reported by parents is the appearance of recurrent leukocoria (i.e., “white eye”) in recreational photographs. A quantitative definition or scale of leukocoria - as it appears during recreational photography - has not been established, and the amount of clinical information contained in a leukocoric image (collected by a parent) remains unknown. Moreover, the hypothesis that photographic leukocoria can be a sign of early stage retinoblastoma has not been tested for even a single patient. This study used commercially available software (Adobe Photoshop®) and standard color space conversion algorithms (operable in Microsoft Excel®) to quantify leukocoria in actual “baby pictures” of 9 children with retinoblastoma (that were collected by parents during recreational activities i.e., in nonclinical settings). One particular patient with bilateral retinoblastoma (“Patient Zero”) was photographed >7, 000 times by his parents (who are authors of this study) over three years: from birth, through diagnosis, treatment, and remission. This large set of photographs allowed us to determine the longitudinal and lateral frequency of leukocoria throughout the patient’s life. This study establishes: (i) that leukocoria can emerge at a low frequency in early-stage retinoblastoma and increase in frequency during disease progression, but decrease upon disease regression, (ii) that Hue, Saturation and Value (i.e., HSV color space) are suitable metrics for quantifying the intensity of retinoblastoma-linked leukocoria; (iii) that different sets of intraocular retinoblastoma tumors can produce distinct leukocoric reflections; and (iv) the Saturation-Value plane of HSV color space represents a convenient scale for quantifying and classifying pupillary reflections as they appear during recreational photography.

Concepts: Cancer, Color, Hue, Color space, Photography, Retinoblastoma, Photograph, Colorfulness


There has been an intense discussion among the public about the colour of a dress, shown in a picture posted originally on Tumblr (; accessed on 10:56 am GMT on Tue 24 Mar 2015). Some people argue that they see a white dress with golden lace, while others describe the dress as blue with black lace. Here we show that the question “what colour is the dress?” has more than two answers. In fact, there is a continuum of colour percepts across different observers. We measured colour matches on a calibrated screen for two groups of observers who had reported different percepts of the dress. Surprisingly, differences between the two groups arose mainly from differences in lightness, rather than chromaticity of the colours they adjusted to match the dress. We speculate that the ambiguity arises in the case of this particular image because the distribution of colours within the dress closely matches the distribution of natural daylights. This makes it more difficult to disambiguate illumination changes from those in reflectance.

Concepts: Light, Color, White, Qualia, Hue, Magenta, International Commission on Illumination, Black


Cytochromes P450 play important roles in biosynthesis of flavonoids and their coloured class of compounds, anthocyanins, both of which are major floral pigments. The number of hydroxyl groups on the B-ring of anthocyanidins (the chromophores and precursors of anthocyanins) impact the anthocyanin colour, the more the bluer. The hydroxylation pattern is determined by two cytochromes P450, flavonoid 3'-hydroxylase (F3'H) and flavonoid 3',5'-hydroxylase (F3'5'H) and thus they play a crucial role in the determination of flower colour. F3'H and F3'5'H mostly belong to CYP75B and CYP75A, respectively, except for the F3'5'Hs in Compositae that were derived from gene duplication of CYP75B and neofunctionalization. Roses and carnations lack blue/violet flower colours owing to the deficiency of F3'5'H and therefore lack the B-ring-trihydroxylated anthocyanins based upon delphinidin. Successful redirection of the anthocyanin biosynthesis pathway to delphinidin was achieved by expressing F3'5'H coding regions resulting in carnations and roses with novel blue hues that have been commercialized. Suppression of F3'5'H and F3'H in delphinidin-producing plants reduced the number of hydroxyl groups on the anthocyanidin B-ring resulting in the production of monohydroxylated anthocyanins based on pelargonidin with a shift in flower colour to orange/red. Pelargonidin biosynthesis is enhanced by additional expression of a dihydroflavonol 4-reductase that can use the monohydroxylated dihydrokaempferol (the pelargonidin precursor). Flavone synthase II (FNSII)-catalysing flavone biosynthesis from flavanones is also a P450 (CYP93B) and contributes to flower colour, because flavones act as co-pigments to anthocyanins and can cause blueing and darkening of colour. However, transgenic plants expression of a FNSII gene yielded paler flowers owing to a reduction of anthocyanins because flavanones are precursors of anthocyanins and flavones.

Concepts: DNA, Color, Flavonoid, Pigments, Flower, Hue, Anthocyanin, Anthocyanidin


Application of pigments in textile coloring has many advantages such as less water and energy consumption, less effluent load and higher efficiency, so the pigments are perfect alternatives to dyes for eco-friendly coloring. In this work, a stable anionic nanoscale pigment suspension was prepared using a polymeric dispersant to color the cationised cotton with the exhaust method. Meanwhile, ultrasound was carried out during the adsorption to evaluate the ultrasonic influences on the uptake of pigment, adsorption efficiency and final product quality. The uptake of pigment is found to be higher with ultrasonic method than that with conventional technique because of the good dispersing capacity of ultrasound to pigment particles. Besides, it is found that nanoscale pigment has higher adsorption rate when using ultrasonic method because the ultrasound promotes the diffusion of pigment through the fiber-liquid boundary layer. Lastly, the color difference (ΔE) reveals the nanoscale pigment can be deposited on cotton surface more uniformly under ultrasonic condition, improving the product quality obviously.

Concepts: Purple, Dye, Pigment, Pigments, Textile, Hue, Form of the Good, Biological pigment


Synaesthesia is a condition that gives rise to unusual secondary sensations (e.g., colours are perceived when listening to music). These unusual sensations tend to be reported as being stable throughout adulthood (e.g., Simner & Logie, 2007, Neurocase, 13, 358) and the consistency of these experiences over time is taken as the behavioural hallmark of genuineness. Our study looked at the influence of mood states on synaesthetic colours. In Experiment 1, we recruited grapheme-colour synaesthetes (who experience colours from letters/digits) and elicited their synaesthetic colours, as well as their mood and depression states, in two different testing sessions. In each session, participants completed the PANAS-X (Watson & Clark, 1999) and the BDI-II (Beck, Steer, & Brown, 1996, Manual for Beck Depression Inventory-II), and chose their synaesthetic colours for letters A-Z from an interactive colour palette. We found that negative mood significantly decreased the luminance of synaesthetic colours. In Experiment 2, we showed that synaesthetic colours were also less luminant for synaesthetes with anxiety disorder, versus those without. Additional evidence suggests that colour saturation, too, may inversely correlate with depressive symptoms. These results show that fluctuations in mood within both a normal and clinical range influence synaesthetic colours over time. This has implications for our understanding about the longitudinal stability of synaesthetic experiences, and of how mood may interact with the visual (imagery) systems.

Concepts: Psychology, Color, Selective serotonin reuptake inhibitor, Qualia, Hue, Synesthesia, Colorfulness, Secondary color


Homogenate extraction technology was developed for extraction of gardenia yellow pigment from Gardenia jasminoides Ellis fruit. The operating parameters affecting the color value of gardenia yellow pigment were studied on the basis of a Box-Behnken design and response surface methodology. Results showed that the optimum extraction conditions were as follows: extraction time 41 s, ethanol concentration 50 %, ratio of liquid to material 15:1 (mL:g) and particle size 1.7 mm. Under the optimum condition, the experimental color value was 52.37 g(-1), which was in keeping with the predicted one. Compared with the heat extraction method, the color value of gardenia yellow pigment of homogenate extraction was higher and the extraction time was shorter. Homogenate extraction method is an ideal means for extraction of gardenia yellow pigment from Gardenia jasminoides Ellis fruit.

Concepts: Color, Operations research, Purple, White, Yellow, Hue, Gardenia, Gardenia jasminoides


We recently reported that an allowed d-d transition of trigonal bipyramidal (TBP) Mn(3+) is responsible for the bright blue color in the YIn1-xMnxO3 solid solution. The crystal field splitting between a'(dz(2)) and e'(dx(2)-y(2), dxy) energy levels is very sensitive to the apical Mn-O distance. We therefore applied chemical pressure to compress the apical Mn-O distance in YIn1-xMnxO3, move the allowed d-d transition to higher energy, and thereby tune the color from blue to violet/purple. This was accomplished by substituting smaller cations such as Ti(4+)/Zn(2+) and Al(3+) onto the TBP In/Mn site, which yielded novel violet/purple phases. The general formula is YIn1-x-2y-zMnxTiyZnyAlzO3 (x = 0.005-0.2, y = 0.1-0.4, and z ≤ 0.1), where the color darkens with the increasing amount of Mn. Higher y or small additions of Al provide a more reddish hue to the resulting purple colors. Substituting other rare earth cations for Y has little impact on color. Crystal structure analysis by neutron powder diffraction confirms a shorter apical Mn-O distance compared with that in the blue YIn1-xMnxO3. Magnetic susceptibility measurements verify the 3+ oxidation state for Mn. Diffuse reflection spectra were obtained over the wavelength region 200-2500 nm. All samples show excellent near-infrared reflectance comparable to that of commercial TiO2, making them ideal for cool pigment applications such as energy efficient roofs of buildings and cars where reducing solar heat to save energy is desired. In a comparison with commercial purple pigments, such as Co3(PO4)2, our pigments are much more thermally stable and chemically inert, and are neither toxic nor carcinogenic.

Concepts: Light, Chemistry, Nitrogen, Color, Blue, Purple, Pigment, Hue


Subwavelength structural color filtering and printing technologies employing plasmonic nanostructures have recently been recognized as an important and beneficial complement to the traditional colorant-based pigmentation. However, the color saturation, brightness and incident angle tolerance of structural color printing need to be improved to meet the application requirement. Here we demonstrate a structural color printing method based on plasmonic metasurfaces of perfect light absorption to improve color performances such as saturation and brightness. Thin-layer perfect absorbers with periodic hole arrays are designed at visible frequencies and the absorption peaks are tuned by simply adjusting the hole size and periodicity. Near perfect light absorption with high quality factors are obtained to realize high-resolution, angle-insensitive plasmonic color printing with high color saturation and brightness. Moreover, the fabricated metasurfaces can be protected with a protective coating for ambient use without degrading performances. The demonstrated structural color printing platform offers great potential for applications ranging from security marking to information storage.

Concepts: Photon, Electromagnetic radiation, Color, Printing, Hue, Visible spectrum, Color theory, Colorfulness