Comment by chambers

I use the "Shortcut" section in Accessibility Settings. I uncheck everything except for "Color Filtering". I then map the default hotkey to a more convenient key using BetterTouchTool. BetterTouchTool is additional software for customizing input devices; I've used it for a decade and I consider it essential.

Sadly, adding "Increase Contrast" to the shortcut causes the hotkey press to generate a voiced popup instead of quietly and directly toggling.