I sure miss the Red/Green combination for the phone app. Green to dial, red to.hang up. This single Red is confusing.
You can always use a Theme.
I'm using HEX on my device running One UI V5.0
I'll add to that the best theme app
Reading their post, "Green to dial, red to.hang up", indicates quite clearly, that it is BOTH calling out and ENDING a call. They didn't mention anything about receiving calls.
AND, it's not so much of a problem, rather it's a visual preference. 😉