I never had a great deal of problems with colour balance when using the cls filter, you just need to back of the blue channel a bit if anything.
Probably a better one to look at would be the IDAS LPS filter like one of theses here.
http://starizona.com/acb/IDAS-C737.aspx
Well worth the dollars for where I live. If I didn't have one, I wouldn't be able to get very long subs at all, probably 50 sec max. When I used a light pollution filter, I can get that out to ten minutes, no probs. Unfortunately, the light pollution filters will inadvertently block some of the light you are trying to record, however as with anything, it is a trade off.
For the QHY8, I would reccommend the 48mm screw on version.
