Good for you, trying to make the cubes work out in your OBW... they are cool. I think the problem with the blue cubes is that the dark is too dark, and the light is too light. They stand out too much from the other values in your quilt. You can use a little less contrast and still get the 3-D effect you want. Could you try finding a lighter dark, and a darker light? Just the blues. The others seem to be working fine.