While I am awaiting a reply from the dev team I would like to document some success here.
Today the colors were fine
Yesterday evening I adjusted the registry to allow for f.lux (see faq for nightlight/f.lux:
FAQ article). That evening the colors were still wrong but the monitor reacted to f.lux.
When I started the PC today (cold boot) the colors were fine, blue was blue and red was red.
I did not restart again today because I am using the monitor for work and didn't want to jinx it, will report back tomorrow if the colors are still ok or not.