in reply to too many colors, using Tk to write images
I'm fairly certain there's no way to create a Tk::Photo without a parent widget, as it assumes a certain amount of context that's provided by the parent.
My guess regarding running out of colors is that the palettes of the GIF files contain slightly different colors, so they can't be combined naively. I don't know which line of the code you posted is line 228 and generating the error, but if it's the copy line, then the redither won't help because the program never gets to that point. Update: The redither won't help regardless, as it doesn't actually reduce the colors used by the image. If I understand the docs correctly, it's for display purposes only.
If it's the write line, then it may be that the combined palettes contain too many colors to be supported by GIF (IIRC, GIF only supports up to 256 colors per image block; though you can do some trickery using multiple image blocks to get more than 256 colors total in the image, I'd be willing to bet Tk doesn't support that).
The best bet I can think of (and, of course, that doesn't mean the best bet in general ;) would be to reduce the number of palette entries used in the original images.
In the end, however, I think you'd be better served by looking into the other image processing modules available, such as Image::Magick or GD, as their more sophisticated features would probably make this job easier.
Good luck.
Update: Oh, and I assume it's just a typo, but you would need quotes around the value you're passing to the palette option for the code to compile.
bbfu
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Fearless on my breath