Single colored LED's like the typical Green and Red are pretty narrow in their output spectrum. They do not line up well with coral pigment absorption lines so, I do not believe they add to coral health in any significant way. One could argue that a deep blue, 410nm, might be beneficial as Chlorophyll A has a 417nm line. There is a red line that is weakly covered by "white" LED's. I am not sure how important that is because in nature very little red hits our corals below 5 meters deep. The "white" LED phosphors cover the other active pigment lines very well.
For appearances... that is a personal preference thing.
edit - oops, rtparty beat me to it.