You will need:

1/4 yard each of 7 light fabrics  –  1/4 yard each of 7 medium fabrics  – 1/4 yard each of 7 dark fabrics.

To make it more coordinated I picked 7 colors then used a 4th yard of each shade.  For example I used a dark, medium and light blue, dark, medium and light green, etc.  I have used the purple and green colors for my samples.

If you buy a half yard you can make a much larger quilt.  Mine covered the top of my queen mattress prior to the borders using only 4 inches more of each than the quarter yard.