Cool skin tone refers to a skin type with a bluish undertone. People typically fall into one of two skin type categories: cool or warm skin tone. Determining one's skin tone will allow them to learn what types of colors look best on them, for the purposes of hair color, makeup, jewelry, and clothing. Cooler skin tones tend to have blue undertones, while warm skin tones have yellow undertones.
There are a few different ways to determine skin tone. The first is to flip the wrist over and look at the veins there. If the veins appear blue, the skin tone is cool. If they have a greenish tinge, the skin tone is warm. Another option is to hold a white towel or t-shirt underneath the face; if the face reflects yellow, it is a warm skin tone, and if the face appears blue, it is a cool skin tone. Finally, people with cooler skin tones may have lighter eyes than those with warmer skin tones, but this is not always the case.
Those with a cool skin tone tend to look better in silver jewelry. They can also wear more stark colors close to the face, such as black or pure white, whereas someone with warmer skin does not often look very good wearing pure white. Cool skin tones tend to look great in "jewel" tones and brighter colors as well, both in clothing and cosmetics. Warm-toned people often look better in gold jewelry and earth tones instead. Foundation for a cool skin tone should have a pink color base.
The ability to recognize the undertone of any color and match it to skin tone is a great skill to have, and will ensure a wardrobe full of flattering pieces. Hair color is similar, and in general, people will look best with a hair color closest to the one they were born with, at least in undertone. A hairdresser should be able to tell you which hair colors have cool undertones and which have warm; this is especially important to match, because a hair color that does not flatter skin tone can appear brassy, and give skin a sallow, unhealthy, and unnatural appearance.
Some people are lucky enough to have a somewhat neutral skin tone, and can look good in most colors. This is very rare, however. In general, it is best to determine skin tone as soon as possible, because it will make it much easier to shop for flattering clothing, jewelry, and makeup.