|Objects as SketchUp displays them|
|Twilight render with issue: background of hexagon should be red|
It turns out it was slightly more complicated than that. To model as efficient as possible I have nested components:
-> Group of 7 components
|--> 1 Fuel Cell Component
|--> Hexagon Component
The reversed face was in the hexagon component which was painted red. The group of 7 components had a default color of white. Once I found a removed the default color from the larger group the hexagons started to paint correctly.
Of course, if I'd paid attention to reversed faces in the first place this wouldn't have been an issue. Also, if I hadn't accidentally given the group a default white color this wouldn't have happened either. This isn't a biggie but it took a while to find out what was going on but it is a lesson learned: keep your reversed faces in order to avoid problems or inconsistencies with materials later.