This might be a common question, but I can't find anything about this problem in particular since Im not sure what this effect is called in technical terms.
Most painted walls I see in real life have, when seen at a certain angle in sunlight, an unevenness to them. In the roughness/gloss.
I see that most skilled 3D artists recreate this in their renders when doing interiors with white walls etc.
I've tried to achieve this in Cycles using a noise node plugged into the roughness. I doesn't seem to be the right way to go though, since other people get a result much closer to reality.
I snapped the attached image earlier today just to clarify what I mean. It's an exterior wall but the effect is the same for interiors. This wall seems to have a flat diffused color when viewed from the front. This effect only shows from this angle.