Well, it was a good idea.... just not executed terribly well.  I tie-dyed the plain white long-sleeved shirts from last Christmas' sheep costumes orange, putting lots of little circles on one and one big circle on the other.  The big circle came out well and was transformed into a Jack-o-lantern for Benjamin. 

But the little circles were not very visible so Jonah's shirt became a big bat.  (both just colored in with a Sharpie marker)   The most challenging part of the whole thing was getting a photo that captured both boys with reasonable expressions and the bat/jackolantern visible.  Out of more than 30 shots, this is the best:

Below, Jonah flying out of his Bat Cave. 

Out for a walk: 

 Happy Halloween!