Subcutaneous fat only allows blue light to penetrate skin all the way to veins, so this is the color that is reflected back. Less energetic, red and orange colours are absorbed by skin before they can travel that far. Blood also absorbs light, so blood vessels appear dark. Arteries have muscular walls, rather than thin walls like veins, but they likely would appear the same colour if they were visible through the skin.
Reference: Kienle, A., Lilge, L., Vitkin, I.A., Patterson, M.S., Wilson, B.C., Hibst, R., Steiner, R. (1996). Why do veins appear blue? A new look at an old question. Applied Optics, 35(7), 1151-1160.
I hope that answers you question…I didn’t know this either!
This is pretty cool – I didn’t know until Roy looked it up either. You have stumped two of us. Interestingly, blue light is the most penetrating, which is why a lot of things seem blue or grey at a distance or looking through water. It is at the high energy end of the spectrum and going towards things like gamma rays that I work with and are radioactive. Gamma rays can travel through your skin and ionise your cells, even causing cancer. They have to be stopped with lead bricks which are dense enough they can’t penetrate. :S
Comments
icecream2311 commented on :
So why do the veins in our eyes stay red is this because there is no fat?
Roy commented on :
It’s more likely just because the vessels are so thin that they are completely see-through.