i guess you could also use the colour replacer tool if there's one available
It wasn't necesary.
Hi, everyone! Finally after several attempts, I was able to make the backgrounds work!
I applied the advice of both Meridian and Warboy, first I applied the palette that Meridian provided me and then the modified palette of Warboy and voilá!
The only one that I could not fix at all, was the one on the research page (BACK05), I hope you can check it to see what's wrong and fix it.