I do use Gauge as it has a nice and easy to understand visual. However, in the above case, it is not ideal to confine the number to a capped upper limit.
Hi there! I think it really is something needed by many other people using or just testing Metabase. I think most people just try the solution and go away if it doesn't fit their needs. They don't come to discussion forums (here or at Github) to talk about what they missed. Just a few of us do that, I guess.
Anyway, this dynamic card coloring is something already suggested on Github in 2016 but, unfortunately, is not available yet. Hope to see this feature in Metabase soon.