For future reference-- DON'T render your planets onto a green background. Render them onto black, do your clipping and resizing, then as the last step before palette-reducing, do a flat green flood fill.
I used to run into this problem a lot with "graphic artists" (aka liberal arts Photoshop monkeys) that didn't understand that key colors had to be precise. I'd constantly get graphics with purple or green thoroughly mixed into the edges. Ugh. These were usually the same people who couldn't grasp why it didn't matter what DPI a screen graphic was.
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ZylonBane's opinions do not represent those of the management.