Palette reduction, I need help

[Sketchasaurus]

The Paint first, reduce later method is a perfectly valid approach to going about creating pixel graphics, especially backgrounds.

The way that you would go about this in graphicsgale is by copying the RGB value of the color you're keeping in your palette (when you set the color depth for an image in graphics gale, you get a palette you can fiddle with) and pasting the RGB value into the selected color that you're replacing it with. after this, in the same window (all of this is done in the palette's dropdown menu when you click the little arrow) you would use the "Unite Duplicate Colors" tool or if you go about changing the colors with the color replacement tool, "Remove Unused Colors" works too (but you have to make sure that the color you're getting rid of is completely gone from the image)