2018 Volume 42 Issue 2 Pages 59-
The blood in veins is red. Then why do veins appear blue? This is one of the "frequently asked questions" on colors. It seems that there are two typical answers to this question. One is that vein is not physically blue. Blue vein is just an illusion(the illusion theory).The other is that vein is physically blue because the blue light tends to be strongly scattered in the skin(the scattering theory).Which theory is correct? To solve this problem, we measured the colors of human arm veins and the Mongolian spot, that also appears blues, by using spectrophotometry. Then, we confirmed that both vein and Mongolian spot were not physically blue. Compared to the surrounding skin colors, they have low lightness and low chroma, but their hues were yellow-red, not blue. Therefore, these results qualitatively support the vein illusion theory. However, what kind of illusion mechanism works should be answered in the future.
