EDITED/UPDATED:
If you remember, I made a post
here a week or two ago looking for answers on how to maintain colors if you have two or more. I got an answer today, sort of. I had a coupon for a free cut at the Gene Juarez Academy and, noticing the colors in my stylist's hair, I asked her how she washed hers. Her answer basically came down to how it's really tricky to do and she usually has one of the other students help her and still occasionally ends up with bleach or dark spots. She graduates in about a month and a half, so she's probably a good source of information on this.
So, yes: Maintaining 2 or more colors is just a bitch, and there's no way to make it any easier.
I'm still gonna keep my brilliant red and pale blonde, because I've never seen a color combination that looked better on me. Well, I'll keep it until I decide I want clearly artificial hair colors again.
This is after I got it cut. The red has really faded down and most of what the stylist took off was the underlayers, which was mainly red. That's okay though, because it's about time to touch it up anyway.