Take a look at the skin on your face and hands. Those with cool skin tones will have undertones to their skin that are pink, olive, dark brown, or bluish. By contrast, those with warm skin tones will have undertones that are peach, gold, yellow, or brown and gold. Ask a friend if you cannot tell your skin tone.
For cool skin tones, you should go for intense shades of red. You can pull off the more wild hair colors such as bright red and burgundy.
Those with cool skin tones should stay away from 'warm' red colors such as bronze or red colors with gold or yellow bases. These can wash out your skin and make you look sallow.
Someone with warm skin tones will look best with warm shades of red. Try a rich auburn, mahogany, or red colors with a golden base to them.
Those with warm skin tones should stay away from bright reds that may wash out your color. Stick with the rich red colors.