It's been on the 'todo/maybe' list for many years but has hardly ever been asked about so I've never been quite sure if it's worth the effort.
What do C16/+4 developers currently use? just native 8-bit tools?
I was using CBMPrgStudio’s sprite/char editor but with each release it gets progressively worse to the point it’s now not worth the effort. Now I use CharPad pretty much exclusively I colour manually which is a bit of effort.