Jim,
If you have the surface ready for paint you might consider using either a cream or light gray of the paint type you will use for final paint. I don't know how heavy the water base paints are compared to dope but if the surface is sealed-water proof then the cream or Lt gray will cover and give a good base color.
With dope after initial sealing and filling, silver was used as the fine filler and surface prep. The silver is very unforgiving and shows every little imperfection (makes you feel like crap, but it is the lightest dope filler you can use for surface prep). The surface issues were filled and all was sanded down till almost all the silver was off. Some finishers gave it a second coat and sanded that off after the surface was to their liking. Then a single final coat of silver was sprayed on as the block. Some other used Cream or light gray color instead of the silver for the block coat.
Best, DennisT
Best, DennisT