Here are my thoughts.
1. I wouldn't put 2 large borders next to each other, even though the one will be piano key style.
2. Put in a 2-3" border of the dark brown? fabric used in the "Dark Block". This will bring out the darks in all the blocks, including the dark block and make it less noticable.
3. Then put in a smaller border 1-1.5" of the tan or even a lighter red.
4. Then finally the piano key border at 4-5", depending on the final size desired.