Mmm, Nipples....
The shade should match the rest of the skin. On a fair skin breast, pinkish is best, or some pale cousin of red or maroon. The darker the skin, the better it matches dark areola & nipples. There are exeptions, for example pornstar Lucy Lee would be fair without tanning, but would look great with her burgundy buttons.
I'm mostly into breasts for the nipple. I like the nipple to almost dominate the breast. This is usally easier on small breasts, they can only get so big before the areola gets to hockey puck size. Alyssa Milano's semi-puffies represent the limit in size for my taste. The gold skin equivalent would be Tia Carerre's juicy brown prunes.
I could live on breasts like those of LucyLee, Sabrine Maui or Nikki Chao. Oddly, wether it's been GF's or strippers, I usually click better with the busty ones, even Asians, so I remain hungry for nipple-heavy small breasts.