The problem almost always occurs with thermal insulation composite systems (ETICS) facades. The surface of these facades is relatively cold; in the morning, the warmer air condenses on the surface – together with microorganisms and pollen that like these damp spots, resulting in dark discoloration (does not always have to be mold). Actually, the only chance is to use fungicidal coatings that must be renewed regularly to maintain effectiveness. Or you choose a dark facade color from the outset (so that you don’t see the stains...).