From what I know of the graphics files, IVAN takes a 16x16 square (the position of which is defined in the script), and dyes what appears to be the greenish parts a certain colour (e.g. the material it is made of). The colour is set in the script files (Material). There are also some colours that are left alone or treated differently by the script (e.g. the yellow on the weird vacuum cleaner backpack).
So the only problem we'd come up against whilst trying to do this is making the IVAN engine look for a 32x32 square instead of a 16x16 one. And of course, we'd have to make the new graphics
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EDIT: Oh yes, one more problem. Making the new graphics using that strange palette the IVAN graphics use is going to be a pain in the arse.