And the scoring is quite generous. For the coupe color I picked vibrant red, correct was some steel gray and I got 60/100 points

Actually I experienced with different distance metrics and settled for one.

I agree.

I remember there were a couple of websites like this, however, with random colors, better scoring, etc.

For example I found these:

https://color.method.ac

https://hexcodle.com (this one has a 10 hour limit per game, ugh)

But there were many others. Ideas? I am looking for something like colorguesser.com.