Mixing warm and cool leds

[videoman]

I have a project that would be using 4 XP-G leds. 2 that are on the warm 3000K side and 2 that are on the coolish 5200K or so. I need to blend the leds so that I can have a color temperature from 3000 to 5200 K and anywhere in between. Along with this I need a master dimmer to control the brightness of the mixed result.Ideally there would be 2 pots, one for the color temp. and the other for dimming.I would like to use the shark buck 3A for this as the input voltage to the unit must be from 7.2 to 18V DC. The only way I see this is to use 2 drivers ( one for the warm and the other for the cool leds) and a dual channel 20K pot so that if I dim the cools, the warms go bright and visa versa, thereby giving me the color control. Now that is the easy part. The hard part is how do I wire up the dimmer so that after the color blend is achieved, I can dim it WITHOUT losing the color that I dialed in. I have been losing sleep over this.