Your snow flake is very pretty - you said it is a lot of little pieces, are you making 1/2 sq. triangles by sewing the two squares together and then cutting those in half or are you making all triangles and sewing those together?
You probably do need the center to be a bit darker. The picture can be deceptive, what I would do is put it up and walk across the room, if you still have the desired effect then the colors you are using are perfect and I wouldn't change a thing. If you cannot see the center pinwheel you may want to change the color.