For a city that was left high and dry over a thousand years ago, it's an awfully watery theme. The blue and red colors are pretty saturated, so the walls could be painted in Whirlpool or Silver Lake to cut the intensity a bit.
There are SO many cute accessories to be found. Since this is a scheme that could work for a small boy AND a teenage boy, the big things could be kept (which is good, since some of these things are a little pricey), and the smaller items switched out.
Your little one will practically be strolling through Ancient Ephesus!