Weathering of Siding on Different Sides of the Barn
Below are 3 pictures all from the same barn that was painted White. You can see the white paint weathered differently depending on which side of the barn it was on. The North Side which received the least exposure to the elements still has the heaviest layer of white paint. The South Side of the barn which received the most exposure has the most faded white paint. The siding is actually white and grey. The West Side and the East Side (not shown) are somewhere in the middle.
This is typical for painted barns, though after enough years even the sides with less exposure will eventually have the paint come off.