We are discussing implementing RGB dataset rendering. The actual rendering functions aren't too hard to change. But we then have to change the renderer plugin to match, which turns out to be trickier (to make all the options work - currently, they all work on 1-byte volumes). If you can live with the indexed color option, I recently added a 128-color "colorscale" option to AFNI. This isn't fitted into the rendering plugin yet, but that wouldn't be too hard, compared to rendering RGB volumes.
bob cox