Value is more important than color.
You can decide you want a "green" color scheme, but if they are all the same value, than you've got mish-mash.
Sad topic but check out this scrappy quilt. It didn't matter what the colors were - there are reds,blues, greens, browns.
And it's fabulous - and ALL about value.
http://www.quiltingboard.com/picture...t-t202633.html
I would suggest sorting your fabrics into light, medium and dark piles, and then go from there.
Your pattern can be constructed based on the value changes as opposed to color changes.