The whole paying thing is a bit of a trump card. And color is good. Also, don't underestimate behavior. Over the long haul, fish with complex behaviors are going to keep you engaged. Also, m/f pairs if that's how the species lives in the wild are great for observing natural behaviors.
For pure color in a 90, I would go with a Yellow Coris Wrasse and a Royal Gramma for sure. Both peaceful and you can see them from down the block. Also, flashers wrasses if you have a good top. I like Blue and Filamented. And of course clowns. Maybe a trio of one of the smaller species of Anthias. I don't know that group well but many others do. Good luck!