I've always said that I don't really care what color a shiny Pokemon is, as long as it looks good compared to its original design, and is something noticeably different from its original color scheme.
I'm color blind, so I've always feared that I've accidentally run away from a shiny Pokemon when I wasn't paying attention, because there are quite a few off the top of my head (like the previously mentioned Gengar, along with others like Zapdos, Elekid, Garchomp, Lillipup, etc.) that are just a few shades darker/lighter, making them easy to miss. At least with something drastic like a bright yellow Azumarill or a lime green Zubat, you know right away that it's special.