don't forget once you get your swapped blocks, if you're are concerned about colorfastness, you can repeat the Heat set process yourself,
most all of the "art" blocks are heat set, so if you receive one that is paint sticks, crayola, or water color, just Iron them with a cotton setting, no steam, with paper towel over the block, this will insure that your block is heat set and should be machine washable.