I heard a long time ago that when making scrappy quilts your eye might see some colors that clash if they are next to each other and this may happen but if you move one of those pieces just a few patches away, they will co- habitate very nicely together.
When I lay out a scrappy pattern and see one color that may look to strong or bright, I add a few more pieces around it that may have some of the same color in it but in a slightly softer shade works to tone the bright one down and also the bright color can be neutralized by adding the color next to it on the color wheel.
If you have a bright green find a scrap that is either blue green or yellow green to place next to it. This causes a blending effect.
I don't know all the color rules o rhow I pick pieces to go next to each other. I tend to use all colors in all tonesa nd shades right next to each other. I don't know if anyone else likes this look but I do.
http://www.quiltingboard.com/picture...p-t204454.html
Peace