Premature and/or excessive lightening of the paint colour, which often occurs on surfaces with sunny south facing exposure. Fading/poor colour retention can also be a result of chalking of the coating.
POSSIBLE CAUSES:
Use of an interior grade of paint for an outdoor application.
Use of lower quality paint, leading to rapid degradation (chalking) of the paint film.
Use of a paint colour that is particularly vulnerable to UV radiation (most notably certain bright reds, blues, and yellows).
Tinting an exterior grade paint using interior grade colourant. For instance, tinting a masonry paint to a vinyl matt colour formulation
SOLUTION:
When fading/poor colour retention is a result, it is necessary to remove as much of the chalk as possible (see Chalking). In repainting, be sure to use a quality exterior house paint in colours recommended for exterior use.