I wrote a script that might fix your tinted screenshot issue
First of all, big thanks to 7empest from Autohotkey Discord for the help with the script.
Anyway, I have created an Autohotkey script for you guys to use. It works really well for me on my Windows 10 1903 atm. I normally take screenshots using the PrtSc button on my keyboard, which triggers the default "Windows Snip & Sketch" tool. Alternatively, I also use the key combinations Windows + Shift + S, which also brings up the same tool as well. The script below is for my personal use, but you can use it as a template and modify it to make it use your own key combinations and run specific screenshot capture tools.
The way the script works is simple. When the key combination "Windows + Shift + S" is pressed (#+s), it brings up the screenshot tool and it will send Alt+End, which basically disables F.Lux. This is the shortcut it uses. Then it will wait until your screenshot tool has exited/terminated, then it will trigger Alt+End again to restore F.Lux back to normal.
I won't provide additional support here, so you'll have to study the Autohotkey documentations if you want to modify the script yourself. Anyway, just download Autohotkey, create a .ahk file and edit the file and run it.
wintitle := "Screen snipping ahk_class Windows.UI.Core.CoreWindow ahk_exe ShellExperienceHost.exe"
WinWaitActive, % wintitle