Unless you have a darker skin tone, I feel that black eyeliner can be a little harsh, and perhaps best saved for a night out. A light to dark brown looks best on light to medium skin tones, especially if you have blonde hair, and green or blue eyes.
Whichever color you choose, take this advice from Cosmopolitan and select a lighter, more subtle color for your bottom lids (if any at all). Keep the liner off of your water line and use a nude pencil there instead to open up your eyes. Also, most women look best with eyeliner only applied to the outer 3/4 of their eyes. There’s no reason to trace the entire eye! It doesn’t look natural.