If you're using PB5.20 then the 2D and 3D sprite commands have been bundled into one library. There is no Start3D()/Stop3D() /DisplaySprite3D commands now, so you can use:
DisplayTransparentSprite(SprintNum,x,y,Intensity,Colour)
I used this technique for the colour cycling on the BigDemo. I can't remember if you need a an 8bit colour sprite for this though off the top of my head. Give it a whirl with the new version (beta 8 at the moment)