Thank you very much! I will have to try it and let you know how I make out!I use Photoshop but I'm sure the steps should be the same with any graphic editor.
My steps are:
1. Pick a reference sprite, usually one from IDLE animation but sometimes from WALK.
2. Save that sprite as say, Map1.png.
3. Open that Map1.png in graphic editor then open its palette.
4. Modify the palette. Change some colors, change brightness, contrast, hue, saturation or anything you want.
5. Save the file (not the palette).
And you have map1.png as alternate palette.