**The phenomenon of contrasting color perceptions of “the dress” photograph has gained scientific interest. The mechanism underlying why individuals differ is yet to be fully explained. We use the powerful twin model design to ascertain the relative contribution of genetic and environmental factors on perception variation. A sample of 466 twins from the British TwinsUK registry were invited to report what color they saw in a standard image of the dress in standard illumination. The mean age of the participants was 49.5 ( SD = 17.8) years, and 85% were female. When asked to choose between white and gold (WG) or blue and black (BB), 328 reported WG (70.4%) and 135 (29.0%) reported BB. Subjects choosing WG were significantly older (p < 0.01), but there was no significant difference in gender. Monozygotic (MZ) twins were more concordant in their responses than dizygotic (DZ) twins (0.46 vs. 0.36). Twin modeling revealed that genetic factors accounted for 34% (95% confidence interval, 5%–59%) of variation in the reported color of the dress when adjusted for age, whereas environmental factors contributed 66% (95% CI, 41%–95%). This study suggests environmental factors play a significant role in how an individual perceives the color of “the dress.”**

^{−2}) in standard indoor incandescent illumination (mean luminance c.40 photopic cd m

^{−2}). They were asked to name the colors they saw. If their response differed from the two common alternatives “white and gold” (WG) or “blue and black” (BB), they were then asked to make a forced choice between these two alternatives. They were also asked whether or not they had come across the image before.

*x*

^{2}distribution, with the degrees of freedom equal to the difference in degrees of freedom between the full and subsequent models (likelihood ratio test). Each model is compared with the full model, and the best-fitting model is ascertained by identification of the model with the lowest Akaike information criterion (AIC). AIC is a measure of the relative quality of statistical models for a given set of data; the estimate is dependent on the number of parameters and the maximum value of the likelihood function of the model. The AIC gives no indication of heritability itself but enables appropriate selection of a model from which heritability can then be extracted. Heritability will then be estimated from the best-fitting model from the total contribution of genetic factors to trait variance, equivalent to A or A + D.

*SD*) age was 49.5 (17.8) years, and 85% were female. When asked the colors of the dress, the majority (298 subjects, 63.9%) said the dress was WG, 126 subjects (27.0%) perceived BB, and 42 (9.0%) chose other colors (listed in Table 1). Of the 445 subjects (95.4%) from whom a response was recorded as to whether they had seen the dress image before, 312 participants (70.1%) had seen it before and 133 (29.9%) had not.

*SD*) ages were 51.5 (17.0) years and 44.3 (18.9) years for WG and BB, respectively. The mean age was significantly older for participants choosing WG compared with BB (

*p*< 0.0001, unpaired

*t*test). The ages of the two groups are shown as boxplots in Figure 1. The proportions of men in both groups were similar: 14.6% and 17.0% for WG and BB, respectively (

*p*= 0.514). There was a trend toward a greater proportion of older subjects seeing the dress as WG, for both men and women (Figure 2).

*p*= 0.938). The concordance (concordant twin pairs were pairs in which both twins saw the dress as BB) was 0.46 for MZ twins and 0.36 for DZ twins. Proportions and concordances for BB are shown in Figure 3.

*SD*) age was 46.5 (18.0) years and 53.9 (17.0) years for MZ and DZ twins, respectively. MZ twins were significantly younger (

*p*= 0.0001, unpaired

*t*test). As response differs by age, analysis was repeated on an age-matched sample of 224 twins (56 MZ and 56 DZ pairs), with the same number of twin pairs per decade. Mean (

*SD*) ages were 52.6 (17.8) and 52.0 (18.0) for MZ and DZ pairs, respectively (

*p*value for difference in ages 0.822). Concordances were 0.48 and 0.39 for MZ and DZ pairs, respectively.

*n*= 184 twin pairs), model selection statistics suggested that the AE model provided the most parsimonious fit to the observed data (Table 2, best fit model highlighted in bold). The AIC values between the models are comparable, indicating that there is little difference in how well the models best explain the variance in the observed data. However, the AIC value for the AE model is lowest (AIC for AE model is 2 lower than for ACE), showing that the addition of an extra parameter (C) does not improve the fit and is therefore not justified; thus, we chose the more parsimonious AE model. In this model, additive genetic factors (A) were estimated to contribute 38.3% to the total variance in response (95% confidence interval [CI], 10.3%–62.1%), whereas environmental factors (E) contributed the remainder of variance (61.7%; 95% CI, 37.9%–89.7%).

*n*= 112 twin pairs), the AE model was again the most parsimonious fit, and heritability (A) was estimated at 47.2% (95% CI, 7.5%–76.9%). This latter estimate entails large CIs, reflective of the smaller sample size used for the calculations.

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*Ophthalmologe**.*

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*New England Journal of Medicine**, 7 (2), 2041669516645592.*

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*Twin Research and Human Genetics**, 7, 41–46.*

*Multiple Sclerosis and Related Disorders**. Richmond: Department of Psychiatry, Medical College of Virginia.*

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*PLoS One**, 73, 271–275.*

*Cortex**, 33, A137–A142.*

*Journal of the Optical Society of America. A, Optics, Image Science, and Vision**, 25, R547–R548.*

*Current Biology**, 20, 137–142.*

*Current Biology*