There are several styles of scrappy! You can do controlled scrappy where you only use certain colors or you can do any thing goes scrappy. I've done both and they all turn out gorgeous.
I did two log cabins that I used an anything goes light/dark scheme with. I just dumped everything in two bags and used whatever I pulled out unless it was already used in the block. Some of the fabrics in those two quilts seriously clashed with each other but gave the quilts a real vibrancy. Don't be afraid to clash in a scrappy quilt!
I did a stunning red and ivory star quilt with about 20 different reds for the stars and over 30 different white on white, white on cream, and ivories for the backgrounds.
I also make a scrappy quilt that is a square in a square block with black sashing. I really play with the fabric combos on that one. It's got 88 blocks so the number of different fabrics is usually well over 100.