Skin undertones are often determined by checking the color of the veins on the wrist.
If the veins look blue or purplish, it indicates a cool undertone.
Cool undertones have hints of pink, red, or blue in the skin.
If veins appear green, it means the skin has warm undertones because the yellowish skin tone mixes with the blue veins to appear green.
Red or orange are not standard indicators for vein checks in undertone tests.
Therefore, blue veins signify a cool undertone.