I tried the blue covers from isspro, and found using only one cover was not enough, and they still looked white. Added a second cover on top of the first, and they were blue, but were way too dark.
Ended up going w/ one green cover per bulb, and they look great. They dont match exactly, but definitely acceptable, and the green is easier to read at night.
You could probably try painting them like said above, and w/ some experimenting, might give you the color you want.