Add text-to-background contrast

[ai]

https://huetone.ardov.me/ has a nice example of contrast widget.

Do we need all 3 values?

[kazerniel]

I'd find it quite useful too if the app showed APCA colour contrast tiers (preferably with transparency support), so I wouldn't need to juggle among 3 apps while figuring out colour schemes. (The other two being Huetone linked by OP, and Myndex's own APCA contrast tool.)