They do, its all in the alloy the blocks are made of, mix in Ti and you will get orange and white. Toss I think Copper and they turn green, and I think it was Cobalt that will turn them blue.
Im just using trailer hitch balls which is a mild steel gives a nice orange glow and isnt a meanace to cars behind us, since the slag usually turns into itty bitty granules that Clay bar removes.
BTW to those who are about to flame....
we do have "block" cars who are in between us and normal traffic.