A: There are many white primers on the market.  Please don't confuse the word "primer" with "topcoat" or "enamel".  The word "paint" is generic for both primers and topcoats.

 

Therefore, to answer your question more thoroughly, there are white primers and white topcoats.  There are also white direct-to-metal (DTM) coatings which serve as both primer and topcoat.