According to most trustworthy (people who have worked at the factory or first owners) information, the side facing the windshield was body color or black. Apparently the paint was very thin on the horizontal "fins" or what to call them, so the paint wore off to reveal primer or bare glassfiber. Many misinterpreted this as the side was painted in another color, and masked it off when their cars was repainted.
Another thing supporting this is that apparently nothing was masked off at the factory when they painted the cars, since you could find overspray everywhere. They simply didn't take the time to mask.