Sun corals are normally a thin orange tissue over a cylinder shaped skeleton. I good way to check health is to make sure that all the polups are extended, this usually is best seen at nigh after lights out. Another ways is to check if thier is any tissue starting to receed. Remeber (if you dont already know) that the polups are individual and need to be feed that way.
that and when the polyps retract sometimes they get an odd looking shape to them but I havent had any ill effects from them doing this. mine do it all the time here is a pic of them. but like mojo said they have to be individually feed the best way that I have (and many others) is a 2 liter coke bottle with the bottom cut off and add the food into the bottle while its over the polyps so the other fish dont steal the food.
mine stay this way all the time and they are feed alot I dont use the bottle now because they are in an area of the tank that the get feed everytime I feed the tank. and the just keep getting bigger and bigger. they look longer than what they are though the rock they are on is at an angle.
yeah that started out with about 4 or 5 polyps about 2 months ago there are more on the other side of the rock but they are just starting to grow and couldnt get a good pic of them. For some reason they are just going crazy.