Using LED lights will prevent any washing out of colors. The reds and blues and greens really pop vs incandescent.
Using pure white LED will make you white pop along with your colors.
But a great way to stand out over your competition and demand a better price point, is to be able to use your creativity.
One trick I'll share: Works well with smaller trees, say 10-15 feet tall:
trunk wrap and branch wrap as much as you can with a solid color LED (Red, or blue look the best) Then, get some clear incandescent C7's and place them in the canopy of the tree.
an easier one. Get a blue flood light and shine them into the trees as well as putting some warm white lights in the tree. You can get away with using less light strands this way and still have a pretty cool look that is cost effective to your client.