I have a new 27 iMac, on which I run Fedora 15 (with no Apple OS)  just boot straight to Linux.The colors are basically accurate to my eye, but the white point is much higher than I'd like (that is, everything is quite blue). I suppose it's 9300K, and may be due to fancy LED backlighting or some such. I don't know; I'm a software guy.I'd like to adjust it to a more comfortable 6500K. In the olden days (including my old LCD monitor), one would just push a button on the monitor and select that from the menu. On an iMac, of course, that's not really an option. Can I do this in software instead?I know that full-on profiling and calibration software runs on Linux, and I may get to that eventually, but for now I'd just like a simple option. What should I do?
How can I simply adjust monitor color temperture in X?
xorg;colors;monitors
Okay, so, the answer is that the redshift program, pointed out by Stphane Gimenez in a comment above, can do this pretty simply. It's meant to do a clever adjust-white-point-over-the-day thing, but it can also be made to do one-time adjustments with the -o flag.The desired color temperature in Kelvin must be given twice because of the time-based features, which is a bit weird but unimportant. And the other stuff is just there to suppress unhelpful-in-this-case informational messages  it's not important. redshift -o -l 0:0 -m randr -t 6000:6000It's also important to note that the code assumes that neutral is 6500. (And experimentally, -t 6500:6500 appears to me to be identical to using -x to remove the effects completely.) On my system, where I think the native whitepoint is 9300K or so, I'm not sure what the actual numbers end up meaning, but the effect of choosing something lower than 6500 is certainly exactly what I want.I was curious, so I looked at the code. Redshift is doing something a bit more complicated than running xgamma  it has a whole color-ramp table, with data sourced from http://www.vendian.org/mncharity/dir3/blackbody/. I'd look into it even further, but I think the next step is going for full-on proper color calibration.