The images are both GIFS; the only app I have that can edit GIFs is GraphicConverter, which is really more a format conversion utility than an an interactive graphics editor, so maybe the problem is the program, not the images. When I open them, the only colors in the color pallet are the ones already present in the file, and I can't get another color into them by copy/paste either. I tried converting them to PNGs and had the same issue. Then converted them to JPGs, and I at last had full color pallates available. Unfortunately, replacing the red with blue turns the entire colored area the same shade of blue, losing all the original's shading. (I did this with the bucket tool, which I expect to change pixels of the same color as and contiguous with the pixel I apply it to.)
So, do I just need a real graphics editor, instead of GraphicConverter? If so, can anyone recommend a good free or shareware one? (Mac OS, unix, or Windows, in order of preference.) Is there some other format I should be looking at, perhaps one where the file format is more-or-less human readable and I could alter the colors by editing hex color codes, which is much more my speed than graphics widgets? Or is what I"m trying to do just not as trivial as I thought it was?