I recently did a mosaic of M33 and as I didn't manage to get convincing colour on NGC 604 and other HII regions I decided to do another mosaic with the UHC filter. I took UHC for the red channel and the luminance for blue and
green. Actually I like this rather easy and "cheap" (only one picture for colour, not three) approach, although of course all it can show are HII regions, not blue clusters of hot new stars that often can be seen in
good colour images.