Determining your undertone

Neutral –  A mixture of cool and warm
 – Some skin tones have a definite pink/reddish tone. These individuals will benefit from a cool foundation. The key to a flawless look is to stay true to your individual colors. Don’t try to mask and change your natural beauty, enhance it!
Warm – A warm base consists of a yellow undertone.

If you are unsure which category you fall under, take a white piece of paper, lay it on a table, and lay your arm on top. (The best lighting to use is natural sunlight. Fluorescent and light bulb lighting will cast an artificial color.) If you are a definite cool (pink) or warm (yellow), it will be obvious. If you can’t decide, your best bet will be a neutral.

Another way to determine your undertone: 
If your veins appear to be bluish in color, you all into the cool undertones. Your undertone has a blue or pink color spectrum. 
If your veins appear green, you fall into the warm undertones. Your undertone is on the yellow/peach or olive side of color spectrum. 
If your veins appear to a mixture or green and blue, you fall into the neutral undertones.