I prefer the colors diagonally with the darker strips on the outside. I think it defines the borders. I really like the idea of black and grey. If you add color, you would probably have to do a lot more blocks to get a balance. If you want to make it bigger, what about a pieced border? Same width, but change colors. Example-on first picture, top row would be white, black and then grey. Right side would be grey then white (see the pattern). Then finish it with a border of black. This should increase the size considerably without taking away from this outstanding image! Great looking top!