I upgraded to android pie on my galaxy s9 plus sunday morning and now I can't tell whose conversation is whose because the names in the conversation tab are transparent. This makes it really hard to use it.
So it sounds like your theme hasn't been updated to Pie. Look for an updated one or revert to default. To fix this issue. Hope that helps!
You may have to look in settings and play with them option, I know Pie is missing some features we was a custom to!
I had the same problem. Try changing to default theme to make sure it looks "normal" then cycle through your themes and uninstall the ones that don't work well. Not all the older themes seem to be fully compatible.