If it's all the same line, which jelly rolls usually are, the fabrics will shrink consistenly and not be a problem. Also, at our quilt shop, we've found those Shout Color Catches are WONDERFUL for washing colors together. I've tossed in reds, whites, darks together and with a color catcher, the dyes don't run onto the other fabrics - only on the color catcher. I don't know how it works, but it does!