That's because there are only a few different colors used for all overworlds. Also, I recommend you use NSE (Nameless Sprite Editor) Classic for overworlds as it has a few more features, the main being the ability to palette edit.
Pretty much you need to change your overworld to fit within the palette of your game, not the other way around, however, you can tweak the colors of the palette if you wish but it will alter the colors of every other overworld that shares it. [QUOTE/]
Thanks for your reply^^
So I downloaded the NSE Classic but how i start the programm? I dont find the .exe file?!:D