Hi hundido,
Thanks for your question.
hundido wrote:
I'm not understanding if sct, in the gui, is controlled by the slider labelled "tint", which I see in my screenshot under the Xrandr, or if there's supposed to be a tab between Xrandr and Screensaver that I don't have. When I click on the sct binaries to try to install them again, my system tells me I already have them installed.
The Xrandr and Sct tabs of the Display Control module are not available at the same time.
Xrandr is the default GUI interface for 'Display Control' as shown in the first screenshot below. After the optional Sct binary is installed you will see a 'toggle' button (also shown in the first screenshot below).
Click the toggle button to switch between the Xrandr and Sct interfaces. After switching to the Sct interface, the GUI will appear as you see in the second sreenshot below.
Both GUI interfaces (Xrandr or Sct) will have the tint and brightness slider widgets to control the screen color temperature and light intensity respectively. If the Xrandr interface does not produce a comfortable screen appearance, then you could toggle (switch) to the Sct interface to adjust the screen appearance in a manner identical to the sepia effect of the popular Redshift utility. Please see the third post of this thread to better understand the relationship between screen color temperature and the visible light spectrum.
If Xrandr or Sct do not produce the desired screen appearance, the following may be helpful. If the laptop supports hardware backlight control, then please set the Tint and Brightness slider widgets of 'Display Control' to neutral positions (tint = 6500K, brightness = 100) and use the Backlight option to adjust the (hardware) light intensity of the laptop screen. Alternatively, for external monitors, some users may prefer the available manual controls for adjustment of screen brightness and contrast.
hundido wrote:
Is Fossapup an xwayland and not xorg pup, because the note said tint won't work in xrandr or sct in xwayland pups, if I understood? If that's what's happening, do you know what is the newest pup sct would work in?
At this time, all legacy Pups (including your installations of Xenialpup64 and fossapup64) use Xorg for the display server. Both Xrandr and Sct are fully functional in Xorg-based Pups. Please keep in mind, the installed Sct binary must be the one available in the first post of this thread.
On the other hand, new Woof-CE Pups (such as Vanilla Dpup) are currently evolving and available for testing but are not yet official releases. These Pups of the future have many new features including the replacement of Xorg with a different display server (Cage compositor running Xwayland).
Xwayland does not support xrandr or sct modulation of screen tint and brightness. In this scenario, only the Backlight option of 'Display Control' is available for the adjustment of screen illumination. However, for those who prefer Xorg, our Woof-CE devs have provided an option to toggle (switch) between the Xwayland and legacy Xorg display servers. This convenient option will ease the switch to Xwayland, if and when Puppy Linux officially transitions to Xwayland.
I hope this helps. 
PupMates
https://www.smokey01.com/radky/PupMates.html