This may seem like a no brainer. Just go to the store, pick up a pretty color, and walk out, right? Wrong. It's clear that not all shades are the same, but what can be less obvious is that not all shades are meant for every woman. I feel that some women have the misconception that they can wear any color they want on their lips. While they have every right to, some shades are more flattering than others. It all depends on your skin tone/undertone. There are three undertones you need to be aware of:

Cool undertone: You can tell you have cool undertones if the veins in your wrist are blue or blue-purple. Lip colors that work best for you are a blue-based reds and pink-based shades.
Warm undertone: You have warm undertones if the veins in your wrist are yellow or olive. The best lip shades for you are orange-based reds, peach, and earth tones.
Neutral undertone: You have neutral undertones if you have both blue and green veins in your wrist. Lucky you, because you can pull off anything!

Keep in mind, you are free to wear any lip color you choose. Just know that there are colors that will flatter your skin tone better than others.