On ios, you can set the accessibility shortcut to enable/disable greyscale quickly. Useful for when you need colour.

Settings --> general --> accessiblity --> scroll to accessibility shortcut at bototm --> choose colour filters

Enabling greyscale itself is in the display accomodations --> colour filters section of accessibility

Once enable, just triple tap home to turn greyscale on/off

At least some android systems have a similar setting.

I am not sure if this is actually affecting my usage, but I only figured this out a couple days ago. My compulsive usage is mostly text, which grayscale has little impact on.