the shortcut for it is alt+shift+Prtsc
It appears that shortcut functions much like Ctrl+Alt+Del, which means it's very difficult to reproduce or intercept(It's designed that way for security reasons).
I tried to find you a workaround, which is a bit of hack, but it does work:
Run application 'cmd'
Pause 0,1 seconds
Move mouse cursor to Application Center
Click left mouse button
Quick Input, 'sethc 251[ENTER]'
The only reason I'm clicking in the center of the window, rather than simply focusing on it using "Display window "cmd.exe" as [Normal]" is that for whatever reason it "shrugs off" focus(perhaps to prevent programmatically inputting malicious commands).
"sethc 251" will toggle between high contrast and the previous theme.
Annoyingly, you can't just launch "sethc.exe; It'll run, but won't actually act upon the "251" command.
Very much imperfect, obviously, but functional.