I usually do 5 thin coats. One angled from each direction and the final one from the top "viewing" angle. This eliminates the shadowing effect the pebbled finish of the vinyl can cause.

I changed some Palomino panels to the Mercedes dark blue and have yet to see any fade or bleed through.

I've never gone from a dark color to a light color. Has anyone done this and what were your results?

The whole trick seems to be to get the vinyl CLEAN and dry! I scrubbed mine 4 or 5 times and did a final clean using a 50-50 mix of denatured alcohol before painting. Using the alcohol or the clean prep seems to eliminate the "fish-eye" effect you can get from an un-noticed water bubble.

Door trim/moulding