You could use any color combinations just make the black and grey in the same colors - one dark and one light. Such as blues with red, green, yellow where the red is. You can also make them all different giving it a scrappy look. This was the biggest eye opener for me. Realizing that I can choose the colors I want. It can give the quilt a whole different look with different colors. I like that block. Can't wait to see what you do with it.