"Minnie Bannister" wrote in message
....
Applied a coat of Sherwin-Williams ProClassic Extra White to a pre-primed
door yesterday (primer has a very, very pale greenish tint) and found that
there are still dark patches showing through.

Shouldn't one coat of a decent paint have been sufficient?

I've never been pleased with a one coat job with even the best paints. A
lot has to do with the prep you did and what color you are trying to cover.
The second coat can be faster and thinner, but it does add something to the
job.