That was in reference to the UI related improvements @fsflover linked. They are specific to Qubes OS and wouldn’t make any sense in a vanilla XFCE environment (e.g. the Qubes App menu, tray menu, Qubes Settings dialogs etc).
In contrast your request is not Qubes OS specific in the least and something that ought to be implemented by the XFCE team upstream and simply integrated by the Qubes OS team downstream.
Seems like support for control of blue light should be native to the OS, since the health benefits for the user are clearly established. It took me years of familiarity with Qubes before I was willing to install Redshift in dom0. It’s the only package I’ve considered to be worth the tradeoff between device security and, in this case, personal health. I now consider it a necessity for the latter.
While I’d like to see Redshift included in dom0 by default, it’s easy to understand why the Qubes team would choose not to include it. That being the case, perhaps a tutorial on installing the package should be included in the official Qubes documentation. This would have alleviated the anxiety I felt when installing the package myself, and I imagine would be a valuable supportive document for those who already use blue light filters on their other devices.