If I always use cold water for laundry, what is the least number of loads I can separate colored clothes into?

I know darks and lights are the general distinctions, but colors don't really fall neatly into those two.

I'm thinking about three piles:

1) Reds, oranges, and pinks.

2) Yellows, Greens, Light Blues, Lavenders, Grays.

3) Royal to Dark Blues, Purples, Blacks.

Is there a way I can have just two piles?

Or can I even put all the colored clothes together? I only use cold water and the gentle cycle of the machine, so that's the most I can do to prevent bleeding, right? None of the clothes are new. I also put vinegar into the final rinse so I don't use fabric softener sheets in the dryer.