Question

why do some blood vessels look blue when you look at them through your skin?
the way that light moves through your skin makes those blood vessels look blue, but all blood is actually red.
the way that light moves through your skin makes those blood vessels look blue, but all blood is actually yellow.
those are veins that are carrying deoxygenated blood.
those are arteries that are carrying oxygenated blood.

Explanation:

Blood is red. Veins may appear blue - green through the skin due to light - skin - blood interactions. Shorter - wavelength blue light scatters more in skin and is reflected back to our eyes, while longer - wavelength red light is absorbed by blood. Arteries are deeper and not usually visible as blue. Deoxygenated blood in veins is still red, just a darker shade.

Answer:

The way that light moves through your skin makes those blood vessels look blue, but all blood is actually red.