How can you tell what your undertone color is? Run a tester lipstick onto a piece of white paper and look, what color do you see besides? It's easier to see on white paper, harder to see on skin tone until it's too late.

What are you looking for? For theory's sake, let's take your favorite brown toned lipstick Your basic lipstick undertones that you might see would be:
 

1. Red/pink: Makes the color seem warmer, but harder and deeper as well. Can also bring out all the red tones in your skin as well so be careful!
 

2. Yellow/orange: Makes the color warmer, and softer. Looks great on warm skin tones, but if you're really pale, can bring out the green/blue undertones in your skin. To be on the safe side, go towards the yellow side, rather than the orange. Too much orange can make skin look gray and sluggish.

3. Green/blue: A way to make a lipstick more dramatic. deeper. Try to stay clear of these if possible, they can make you look like you're STILL standing under fluorescent lighting.

4. Silver/grey: Adds shimmer, softness, depth, easy to spot in those light shimmer lipsticks that are so popular now. Adds light and softness to the lipstick, just make sure that it's not too much on the blue/grey side. Can make those under eye circles stand out.

5. Green: Huh? Green? Yep, sometimes. The trendy colors have them, and it's usually paired with a yellow tone as well. You'll look cool and hip, but you'll also feel as if you need more color on your face. (Hint: that's why the big blush trend is also prevalent.......just check out the lip color!)

Lipstick Rule Of Thumb:
Whatever skin color you have that you don't like (like blue or grey under eye circles, redness, pink, etc....), try not to copy in your lipstick color or undertone as well. It's like wearing a red dress with sunburn. It just makes the problem appear worse than it is.