[Solution] One of the scenarios where the monitor can't adjust the brightness

[XMuli]

After reading Common reasons for monitors not being supported or detected thought I could add one.

It was found that monitors in one of the Color Gamut & Color Temperature modes would not be able to adjust the brightness using
twinkle-tray; switching to another mode would do the trick. Suggested adding to the wiki

[xanderfrangos]

Thanks for the tip! I'll add this to the wiki when I can.