I don't mean what is your favorite color, I mean what color of lipstick, eyeshadow, or clothing looks best on you? Do you know? To be honest, I'm not positive. I know what my favorite colors are, but sometimes when you look at pictures or video of yourself, you discover that those colors don't always make you look the way that you want to look.
The way that you want to look is the biggest thing - how do you want to be perceived? Fun? Sophisticated? Casual? Smart? There are endless possibilities, and how you want to be perceived can change several times within one day. How I want my fellow yogis to see me is different from how I want a co-worker or lover to see me. Some days I feel confident and want a bold lipstick color, and some days I honestly just want to blend in with the crowd, so I go with a subdued color.
This is where experimenting is essential. If you've never played with different looks, especially with your make-up colors, I highly recommend it. For example, I love dark lip color, but I know from looking at pictures that they make my lips look smaller and can make me look severe, especially if I'm not smiling. Sometimes, for instance if someone has made me angry, that look is fine. In general, though, I want to look approachable and attractive. So if you always stay with the same colors, try some different ones, in your make-up, your jewelry, and your clothes. Take pictures with different color combinations and look at them objectively to find out if how you feel on the inside is the same as what you show on the outside.