Image compositing

This isn't exactly a database question, but I would guess that it pertains to a lot of people's database projects. Has anyone been successful with image compositing of the following general nature? I have a set of many dozens of images which depict various combinations of shapes/styles for products, each of which can be obtained in dozens of colors. I want to be able to keep the shapes in a database, and colorize them with PHP on the fly. Take, for instance, a zebra-stripe pattern that can be shown in white/black or green/yellow, or any permutation using dozens of colors. The object in question is an irregular shape and I can generate the two basic images (the stripes and the inverse of the stripes) with transparent backgrounds in PNG. If overlaid by the browser, BTW, they work fine. However, what I want to do is take the stripes image and colorize it, the inverse-stripes image and colorize it, then composite the two images, retaining the transparent background. I have looked through all the GD and PHP image functions and although they are promising, they don't seem up to this task. I looked at ImageMagick, but I am not sure I can install this, as I am on a hosted server, and I cannot tell whether this task is specifically covered by ImageMagick. Any and all help would be greatly appreciated. --Dave Shugarts