OK, despite what I said earlier, I’ve given this a shot, and I have a working implementation that you can try out if you’re keen (beats marking courseworks for a couple of hours…).
You’ll find the implementation on this branch. You can install it if you have an install from source, following these instructions:
cd mrtrix3 # edit as appropriate
git pull
git checkout mrview_custom_colourmap
./build
Refer to the pull request for details on the format for the colourmaps, but it’ll hopefully be fairly simple to use. Feedback welcome!