That washed out look is common if you just print regularly. I don't adjust my settings when I print - I know some on here print darker to make it look better, but IMHO that makes the print look dark and muddy... with minimal gain at night.
I think the best thing to do is print on clear as a "color bump" on the inside of the face. You don't see the added color during the day, but at night you will definitely see a difference. We mount the print on the front first, then apply our reverse-printed clear vinyl on the inside. We use a light behind the face for line-up, but the lineup doesn't have to be exact - just pretty close.
The only color I flat hate to print is black backgrounds. No matter what you do (short of using black vinyl), it looks washed out at night.