ELECTRICCATGUY'S PROFILE

im trying to make something in rpg maker 2003 and ive already made a custom sprite sheet by editing some already existing sprites, i used medibang paint for this but when i save it and try to import it, it tells me that the image isnt 256 colors ? im not sure what this means and how to fix it?


this is the sprite sheet im trying to use (i only edited the set of sprites in the bottom left corner)
im also saving it as an .bmp because thats what it showed as when i opened it in my art program, should i be using a different program or something else?