Just some food for thought here...
This is a photo from a Japanese LED reefing site showing the spectrum of the sun, along with (what I believe to be) the spectral peaks for optimal coral coloration.
For comparison, here's what cool white and royal blue looks like according to the same website:
It's a little ridiculous to
expect good results in terms of color when so much is lacking here. Mainly, it's lacking ~650nm, ~420nm, 500nm and in UV. As opposed to RGB, I would suggest
adding a deep red LED that peaks around 650nm (ex. the Osram 660nm 3w- most commonly used red LEDs are in the ~620-640nm range, so they won't work for filling in that gap),
an LED that peaks around 420nm (the SemiLED BlueViolet is the only one I know of- 415-420nm),
and an LED that peaks around 500nm (the 3w Cyan Rebel is the only one I know of- the "Cree blues" commonly used to fill in this gap are 465-485nm, which won't completely work). I'm not completely sure about the need for UV yet (I haven't done enough research on this, although I've heard that the colorful coral "sunscreen" is in fact transparent- but again, I don't really know). However,
these 3 LEDs (when mixed with Neutral White and Royal Blue) should give stunning results for coloration/aesthetics.