The simplest test uses a plain white piece of paper. Hold the paper up to your face and compare how your skin looks in contrast to the paper. If your skin looks yellowish, greenish, or light brown, then you likely have a warm skin tone. If your skin looks pink, rosy, or blue, then you have a cool skin tone. If your skin looks gray or ashen, then you are a neutral skin tone. If you have a skin condition like acne, rosacea, or if you are extremely tanned, ask a friend to use the paper test on the crease behind your ear instead, which is less likely to be affected by these variables.
Next, flip your hand palm up and take a peek at your veins in the hand and wrist. If your veins appear to be blue or purple, you have cool skin. If they appear green, then you have warm skin. If it's hard to tell one way or the other what color they favor, then you have neutral skin.
How does your skin react to the sun? People who tan easily instead of burn usually have warm skin tones. People who burn rather than tan usually have cool skin tones, although sometimes women with dark ebony skin that doesn't burn can also have cool undertones. People who are neutral may fall into either group with regards to tanning or burning, but neutrals will not have any obvious appearance of olive, yellow, or ruddy skin.