I usually balance out blues (a cool color) with pinks/reds (a warm color). Blues can also work out well with yellow for a "country" look.
I have lots of brights and personally would probably not try to mix them with muted civil war type patterns, at least not unless it's a very scrappy quilt and the individual pieces are quite small. This is not so much because the colors are different, or even that the patterns are different, but rather because the intensities are so different.