I have a royal gramma myself, and he's in my tank with an ocellaris clown. They are very peaceful and mostly do their own thing. Mine was REALLY shy at first, but they get better and they do swim around a bit. They are not very active, but you will see yours moving around and may times just lounging somewhere in the tank. Mine has a little cave it loves to hide out in, but it does come out fairly often and swim around with the clown. As a comparisson, though, my clown comes up to the top of the tank and eats his food off my fingers as to where the gramma hides in his cave and generall dissapears if my hand goes in the tank.
They are very beautiful fish though! Very colorful and nice to look at, I highly reccommend it. I had a yellow-tailed damsel before, and unless you won't be bothered with its agressiveness, I strongly advise against it. They are the most "peaceful" of the damsel but can still get agressive, I had to take mine back because it would not leave my clown alone.
Hope this helped!