For Blue Eyes:
Shades of brown, camel, and taupe will help blue eyes appear even bluer. The darker the liner, the more your blue eyes will pop, like with dark browns, blacks and charcoal. If you choose a green liner, choose a darker green like dark golden green or forest green. Too light of a green color will not accentuate blue eyes, but make your eyes fade. Also avoid blue liner unless it is super dark navy blue.
For Brown Eyes:
Shades of slate blue, gray, and plum will help brown eyes stand out. Brown eye girls are very lucky. Brown is a neutral color. Thus meaning almost any makeup shade look great on brown eyes. Choose "warm" toners like golden browns, deep red plums, Bronze to make eyes look warmer and softer. Choose "cool" tones like black, deep navy blue, cool dark browns, dark metal grays to make your brown eyes look cooler, and sometimes darker. Avoid light colored liners like light pinks and light purples.