It's typically yellow, blue, or white that I choose as a color blind person. It depends on the other colors available, too.

For example, I choose white in Settlers (the 5 & 6 expansion colors are awful for color blind people, by the way). The other colors look the same as at least one other color (or more in the 5 & 6), and I typically don't care much about distinguishing opponent pieces. There's not a ton going on, so it's easy to remember that Bob has a road around the ore. Also in Settlers, we place the hexes upside down of either the grain or sheep because I can't distinguish them. We place the brick and wood hexes in opposite directions, respectively, so I can tell that wood is the pattern going sideways, brick is going vertically. Just an example, I can't remember what the patterns actually are.

Yellow in Ticket to Ride. I do care about opponent pieces here. I mix up black and red, the blue pieces can blend into the map, and I think there are green and orange pieces that I can't distinguish. Maybe it's blue and pink. I forget the colors.

Blue in Carcassone (the yellow pieces actually blend in to the tiles for me, as do green and orange). With certain expansions (the one with towers, specifically), it's a bitch to see the special features on the tiles. Forget about remembering them twenty minutes later in the game.

Most every game has blue and yellow as options, and both are workable for me, in the event that you have some guy that has a hissy fit if he can't be his favorite color. Not saying this is you at all, but I've had a guy literally pack a game up and go home because he wanted to be blue, despite it being the only workable color for me in the game. Don't ever be that guy.

Anyway, very generally speaking, I prefer white (or purple, but very few games have purple tokens. No idea why purple works well for me.). White gives me contrast against the game board, opponents tokens, and my own. Blue and yellow are typically acceptable second choices.