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.

Taken from the middle of Berlin with an 8"LX200 at f/4, MX716 camera, L-UHC-L-L mosaic with 3x10 minutes for each luminance field through the Astronomik City Light Surpression filter, and 1x10 minutes through the Astronomik UHC for the red channel.