This kind of attitude in OSS is exactly why GIMP is a piece of garbage that no one uses.
How do you do the solid color background in Gimp? In Photoshop, I'd select the background with the magic wand (contiguous or non-contiguous, depending on preference), potentially use one of those edge-improving tools, then either press delete or create a mask. It apparently also has a special tool for it that I haven't used before but seems to do basically that.