My design wall is 6ft by 6 ft. We covered the core board with a thick batting and then used a tan or creme colored flannel but that is the color that went well with my sewing room. Now that it is said and done glad I went with that color cause when I put something up on the wall if it had been a brighter color may have shown thru the blocks. I like it.
Hubby used big washers about big as a fifty cent piece behind the screws that hold the board on the wall to keep the screws from working thru the core board. He found creme colored spray paint that matches perfect and sprayed the washers so they blended with the hardware that keeps the board on the wall. Then he punched a hole the size of the screw head in a piece of paper and spray painted the head of the screw thru it after he had it all up on the wall. So ALL the hardware matches the design wall. Just sharing a few tips.
Corry