This is an extract of a post I made in another forum:

"I had similar problems. My Cintiq 12wx colors were always different than my main monitor ones. I have a very good monitor: an EiZo s2431w, so I always trust him regarding to color reproduction. After I bought my tablet 4 years ago I fiddled a bit with the settings box to get the best calibration for it but as I guessed It's better to set it at default in regards of the brightness contrast department or else I noticed a loss in dynamic range. I was still unhappy with the color inaccuracy and yesterday I took a look at the settings box again and I discovered I had the color temperature at 6500k. I changed it to Direct instead, as I have my main monitor at that setting too, It seems to produce more accurate and vibrant colors, and I finally was able to get correct yellows and reds. I was entirely not satisfied with the vibrancy and I went to my Nvidia drivers and raised the Vibrancy of all the colors from 50% to 62% now the major part of the colors match! but I could not get (and I tried for hours) the magentas and violets to match, It was impossible after tweaking the R.G.B values independently so I think that is the achilles tendon of the 12wx, but I think it's not bad for a 4 year old monitor, I just wished they picked a more accurate Ips panel at the expense of response time, but I'm not sure if it was possible or affordable. Anyhow good luck with it."