JimH told me to create a new thread for this:
All video is coming out with gradiation in the colour. It has the appearance of the video card having a low'ish colour depth. Not as low as 256 colours, but not as high as 32K either. It's definitely noticeable but not movie-killing either.
the same videos show no such colour gradiation when played in MC13 or in several alternative players including Media Player Classic.
I use ffdshow and coreavc as my filters and Haali is installed as a splitter (though I'm not sure if it gets used in all cases or if MC does some splitting on its own). The issue occurs both under ffdshow and coreavc, and as such seems unrelated to filter settings, which btw, were imported from (the working) MC13 via a registry key copy.
So it definitely seems to be an issue with MC14 in particular. If there are any settings related to this please advise.