I used a Luxeon Tri-Rebel star LED array like this one:
The Cree version would also work:
http://www.ledsupply.com/leds/cree-xpe-indus-star-rgb-high-power-led
The Custom Saber Shop sometimes has a version in stock with a deeper blue LED. I haven't tried it, but some claim that it makes a better purple when the colors are mixed with red.
http://www.thecustomsabershop.com/Luxeon-Tri-Rebel-Star-P777.aspx
Depending on the color, max current on these kinds of LEDs can range from 700mA to 1500mA. You shouldn't have a problem finding FETs to handle that. Mine are rated for something like 18 amps!
Also, I am noticing I made an error on the diagram. The negative for the WT588d should be on the far left pin at the top, not the right. I'll try to get a fix up for that tonight when I get some time.