So I'm trying to create a grp file. I made a bitmap image, converted it to a grp, and put it in-game to test. It turned out to have really funky colours. I opened the GRP with PyGRP and saw this:



That's pretty much it. What am I doing wrong?

You need to make the BMP have the SC palette. Easiest way is to extract a GRP from SC, convert to BMP, and paste your BMP on top. Save, rename, and convert to GRP.

That and don't use GRPEdit.

Use SFGRPConverter.