What you're asking has nothing to do with dick, you're really trying to ask what race we prefer.
If I went by actually color of penis, I much prefer a natural color that matches his skin. Nothing he's pumped and bruised, shot up with silicone and made to look like a weeping wound all discolored and angry.
Leave the dick alone. Keep it clean and healthy, and absolutely any color is fine.
Although, now that
@MickeyLee brings it up, I would like to see a blue one, or maybe something that glows like a lightsaber.