Sometimes it's impossible to tell the difference between a new notification that's highlighted and a old notification that's unhighlighted. Hear is a attached image showing the difference between a new notification that's highlighted and old notification that's unlighted, I put a black boarder around the highlighted notification to make it easier to spot.
It's not too bad most of the time for me, but occasionally I struggle.
I think it needs to be a different colour. Because girls are pink and boys are blue and those are the theme colours, they've tried to just scale it down. I think it needs to be a whole new colour so it's not watered down as much. Purple could work, or try incorporating the current orange.