Do you know the age of the stucco? Is it lime, or Portland cement based? If
the stucco is indeed lime and sand then the addition of even latex paint will
eventually cause problems. You are basically applying a skin that will not
allow the masonry to breathe. I would try a lime wash also known as white
wash. There are several places that sell pigments that you can add to achieve
the color you desire. I would not apply anything to the stucco.

Steve