In article , Minnie Bannister wrote:
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?

If the can claims one-coat coverage, then, yes. But I'll bet the directions
say to use two coats. And you just discovered why. :-)