Ok, ImageMagick comes through, but in a way not entirely but almost, intuitively. First, I tried a batch file so I have an editable drop target that would make both pngs and bmp for testing:
(WARNING: the following will make most sense to those familiar with
ImageMagick)
convert.exe %1 -background "rgb(213,204,187)" test.bmp test.png
Ok, the bmp turned out black on the proper background (not good) and the png looked good but there was something... I opened up the png in Ultimate Paint and there was my original png simply pasted on a background with alpha channel so it
looked right, but it wasn't what I wanted. I wanted it mapped on the background so there was no alpha channel left, but the transitions to the background present. I tried all kinds of -channel operations and looked at the forums and in TFM stumbled on:
convert.exe %1 -background "rgb(213,204,187)" -FLATTEN test.bmp test.png
This is supposed to work on multiple images pasted on each other, so I thought I'd try it to 'flatten' my png on the background. TaDa. But the bmp was fuuunnnkkkyyy. Seems as though it was trying to write a 32-bit bmp when I can only deal with 24-bit or less. Tried -colors, -depth, nothing worked. Once again some rummaging around brought up:
convert.exe %1 -background "rgb(213,204,187)" -flatten +MATTE test.bmp test.png
apparently this had nothing to do with what I wanted to do, but it DID remove alpha channel information completely, so my bmp was properly 24-bit. Also, I discovered that the alpha channel HAD to be removed before the -colors option did anything. So now I have my batch code
convert.exe %1 -background "rgb(213,204,187)" -flatten +matte -colors 65536 test.bmp test.png
which can now be imported to a script where I can properly selectify my every whim. Thanks all for the encouragement to stick with IM and when I get a proper code worked up, I'll post it.