Mr./Mrs. Toaster:
In another msg on this board ("57Mb? Really?..."), the author says that they recoloured concrete by adjusting [existing] colours and having to save many images. If you are able to understand basic I/O coding, you may be able to find the section where those bitmaps are called. If you backwards work that and put the section in the right spot, as well as edit all of the [regular] basic grey concrete colours for each colour that you want by adjusting the RGB in an external image editor, then making sure the code can read all of those variations you've just created.. then it "might" work.
Sincerely,
FORTRAN user