I'd say your Duncan is wanting more light. Move it up some in the tank. This is especially true for the other Duncan you shaded from the light. A 4 bulb t5ho can support easier Lps
like this, it just needs to be mid range in the tank. This should begin solving the color issue you are having as well as see more extension from the tentacles on the polyps.
Side note, how is the flow in the tank? These guys like their tentacles to wave gently and it doesn't look like they get to at all. Increasing flow may also be of benefit.