A border would set them off just like a frame does for a picture. However, if you don't want to do it it looks good the way it is too. If you wanted you could just use black or a dark brown and put an L around two sides of each block. The width of your strip down from the top and in from the edge so that it looked like a shadow and that the blocks were actually floating above the background. Like this one:
http://www.quilterswarehouse.com/P-5...uiltwoman.aspx
ooops, I guess this is the same idea as the one before me. sorry.