Longtime user of flux (probably 5 or 6 years on personal and work computers). I am a software engineer with eye issues that cause extreme sensitivity, and so I usually keep it around 2700K all the time.

I am using Flux v4.74 on an up to date Windows 10 laptop. I use a docking station and a dual monitor setup. I have used various dual monitor+docking station setups over the years with Flux v3 without issue. I had been using Flux v3 on my current setup for over 1 year without issue.

The v4 version of flux's 2700 K setting appears to be warmer than the v3 version's 2700 K setting. I have compared them side by side. The v4's 2700 setting (incandescent) appears more comparable to the 3400 (halogen) of v3.

I also verified this manually using a color temperature approximation found here https://academo.org/demos/colour-temperature-relationship/ . Of course, screen color temperature includes brightness - but you can manipulate your RGB ratio manually to get a pretty good approximation.

When I manually manipulate my screen (change RGB ratio) to the approximation for 2700K {rgb(255,167, 87)}, it is absolutely much coolor than the v4 2700 setting. It too appears close to the v4 3400 setting.

I have used the manual manipulation in work settings without flux, and it always matched the v3 pretty accurately. As described above, v4 appears "warmer" for given Kelvin numbers.

I want to use a program that is accurate to the Kelvin numbers, as that is the only way I can get a reproduceable setting across different monitors.

Were there any changes in color temperature rendering between v3 and v4? I certainly see some differences looking through a couple avenues (described above).

Thanks