Found the DP solution:
1. From MISC choose Fg<->Bg Color, then Pict
2. Swap the two colors in the palette editor
For ImageMagick I am looking forward to seeing your solutions!

ALT

@root42 Looking at that partial screenshot, it's the weird MS-DOS version of DPaint, or am I mistaking? 😃

@root42 😁

It's weird because it's like DPaint 2.5, with more colors than the OCS Amiga DPaint III version had at the time, but without animation, which DPaint III did have. 🙂 There has never been another MS-DOS version either. It's an orphan nephew of the Amiga's DPaint. 😉