Check this out. Programmable LED outdoor lighting.
cheaplights(dot)com and locate section 114 on the left
(then scroll down to the 114-LED-OUTDOOR6-L)
These lights have Red, Green, and Blue which when combined at full power, mix to create white. By adjusting the brightness of each color you can create any color on the spectrum.
I'd imagine you would have them on white 300 days out of the year but it might be fun to use the colors on holidays. You can buy a controller to program elaborate light shows or you can manually set the color using the dip switches on the back (there should be a list of dip switch color configurations in the manual). There are four connections to each light: power in, power out, DMX in and DMX out (which is simply the same connection a standard microphone uses). If you have a controller or if you manually set the dip switches on the first light to a certain color, then the rest of the lights on the chain (of your DMX cables) will follow suit. Each light may be powered individually or chained up as well. Pretty simple stuff.