The shading was added by adding cobalt blue, to the direct light color (Top color) to the medium side and then more cobalt for the shade side. Where necessary, I added prussion blue to intensify the dark. I should have color balanced because the table cloth is white. The shadows were created by adding the complimentary color to the block in shade.
1st painting Backlit. Strong Colors with backer wall. The red block is floating a bit. I tried to correct on 2nd picture by darkening the lowest area of the shaded side.
2nd Photo. Backlit, lighter colors. Two big changes here was the addition of reflected color and varying the side colors to allow the block to appear more natural.