I think your painter made a decent suggestion because its a solid color. It will save him work, cost of paint will be less, and he should be able to do the whole job for slightly less money.
A well done single stage can look as good as you would like and the wet look that clear over it gives is hard to see until you get close to it anyway.
Clear over darker colors is easier to see.
I did a single stage burgundy on a car in the 80's. Color sanded it, buffed it,and it still looks great.
If I was doing a solid yellow my choice would be single stage.
Dan
