Color Scheme Help

Hello, long time user proudly working in my 4th Jetbrains IDE. One thing I've never had much luck with is finding the names of color keys that aren't immediately obvious. In this specific case you can see the autocomplete menu open - the first item ("transform") is highlighted. I'm looking for a way to change that highlight background color as well as the overall autocomplete menu color but havent been able to figure out how. Can someone please let me know what it's called? Thanks so much