Thanks for the reply. Yes, I am aware of being able to just extract or grab one of the bands from a multi-band image. I'm not sure that will what I need.
More specifically what I'm looking for is a batch way to reduce the color depth of many multi-band images.
For example, a useful application of this is for scanned map images. Many people who scan them do so at high color depth settings (like 32K or 62K colors - 24 bit) when all they really need is 256 or less colors - 8 bit). These high color images take up 3x as much space (or more) to store all those extra unnecessary colors. In some imaging programs I've seen options to "decrease color depth" which basically filter the colors from all bands down to just 256 or less using some kind of algorithm. This would be a GREAT tool addition to ArcToolbox.
I suppose I could just take one of the bands (R, G, or B) and apply a color map to it to make an indexed color 8-bit image, but I don't think that will work properly, and I'd have to make a colormap on my own.