Definitions for "DISCOLOURATION"
Unless one takes precautions, paint applied over bitumen will develop brown stains because the relatively volatile components of tar or bitumen will permeate and migrate through the paint. Pigment and dyes used in some paint formulations are not colour fast and not intended for exterior use. If these are used outside they will fade. Also the alkali and moisture in newly plastered walls or new concrete can react with paint pigments and cause colour changes.
Natural colour changes.
a soiled or discolored appearance; "the wine left a dark stain"