Yeah, it's not the fact that it's B&W/color, but that they have to transform from B&W to color ON STAGE.
And in City of Angels, hair and make-up was all in color, while Pleasantville would require EVERYTHING (including make-up, hair, and tongues) to be grayscale. It's totally possible to do that, but it's just a nightmare changing from grayscale to color in front of an audience.
But imagine how cool the tree exploding on stage would be. Hot.
Eeeeeeyyyyyyyyaaaaaaaannnnnddddd aaaaaaaiiiiiiiiyyyyyyaaaaaammmmmmmm teeeeeeeelllllliiiiiinnngg yyyyooooooouuuuuuuwwwaaaahh...