Visionaire Studio v4.2 Indexed PNGs work fine for backgrounds, but when loaded in for character animation appear with artifacts. RGB PNGs load just fine.
No problem for me with PNGs. Make sure they are 8 bits, not 16. I had glitches at some time with 16 bits/channel. You can also try the webp format which is recommended by the Visionaire team.
Well indeed indexed animations are not working, but you can still use it after converting to RGB. Create your PNG with indexed colors, convert it to RGB 8bits, and the result is the same, except that it works in VS.