same here in Version 15.4 (17613.1.17.1.6).

well, the usual of course. after posting, i find my way :D first i found NSScreen: https://developer.apple.com/documentation/appkit/nsscreen that says it's just to grab info, but if you need to change, you need to check for Quarts Display Services: https://developer.apple.com/documentation/coregraphics/quartz_display_services so here you go. Quarts Display Services seems to be the thing to change the Gamma colors.