I'm not good at all the math, but I think I would divide the block into 16 four and a half inch blocks.... the four corners, white squares; all the others, half-square triangles. I wish I could send a picture.
w p/w w/p w
w/p gr/bl bl/gr p/w
DOES THIS MAKE SENSE?
w/p gr/bl bl/gr p/w
w p/w w/p w