It was 'messed up' porcelain before... it was very etched and it just
wasn't looking so hot.

The paint is more of a cream color than yellow...it's just that I've
just put in some trim that I painted with the same gallon of paint, and
it is a few shades whiter than the tub. If it is the paint causing
this, than I guess I'm just going to have to accept a cream color
instead of the gleaming white.