Women Painters.com: Paint Issues and Fixes:
Surfactant Leaching
Concentration of water-soluble ingredients on latex paint, creating a blotchy, sometimes glossy appearance, often with a tan or brownish cast. More likely with tinted paints than with white or factory-colored paints.
Possible Causes:
- Painting in cool, humid conditions or just before they occur. The longer drying time allows the paint's water-soluble ingredients - which would normally evaporate, or be leached out by rain or dew - to rise to the surface before paint thoroughly dries.
- Mist, dew or other moisture drying on the painted surface shortly after it has dried.
Solution
Avoid painting in the late afternoon if cool, damp conditions are expected in the evening or overnight. If the problem occurs in the first day or so after the paint is applied, the water-soluble material can sometimes be rinsed off rather easily. Fortunately, even more stubborn cases will generally weather off in a month or so. Surfactant leaching should not affect the ultimate durability of the coating.