Ok, dumb question time! How are trolls grey if they have different blood colors? Wouldn't it show through the pigment of the skin? (this is a Karkat based question btw)

When Trolls blush, their saliva, their eye color when they become adults and their irises fill in, tears, and probably just every bodily fluid in general is Blood-color-tinted. However as long as they’re not actively blushing, it’d seem Troll skin… Or… Chitin? Doesn’t show the color through.