Anything goes. Just make sure you have some light, medium and dark colors to make it look interesting. If it looks too busy to you, add some sashing and borders in solids or blenders. The main thing is that you like it when it's finished.

I pretty much do all scrap quilts, and agree that Bonnie Hunter's site is excellent......have used lots of her ideas.
Color isn't as important as values of the colors is what I have found.

I'm working on a scrappy string quilt. Not impressed with the results.
So, I'm going to sash it and think that will straighten it out. Its going to be donated but I do want it to be attractive. The next one I'm going to do one color with either a punch of white or yellow.

I made a bow tie scrap quilt. The blocks were white with a different color bow tie. Sure used up lots of scraps.

Here is some really good advise on scrap quilts

http://www.quiltingboard.com/t-127283-1.htm

Love the colors! How do you make it without batting?

I really love all types of scrappy quilts. When I make one, I seem to need one color to ground all the other busy ones, a place that lets the eyes rest. I find the more variety, the better the quilt. You will never have a failure with a scrappy quilt.

I think the quilt in my avatar is an example of what you are saying about the sashing ... remember - - as we build a quilt we are really a lot closer to the product than even the next owners will ever be. This causes us to devalue the beauty (one wrong color strip in the wrong place tends to warp our outlook, I think) ... always look at things from a distance to get a better perspective <wave>

a bigger picture of my avatar - - a strippy quilt with sashing <wave>

Here is a good example of a controlled scrappy quilt. I made it for my DGS, he wanted orange, but I had to add some greens and blues and blacks to break up the color a bit and add some interest and definition to the pattern I wanted.
So even tho it's scrappy, I controlled the number of colors and used a definite overall pattern, tho I didn't control how the colors went together in the strip areas too much.