Not sure why'd they be either. If you mean simulating that high points tend to be shinier with higher specular reflectivity then yes they'd appear lighter at certain angles. Also convex high points like ribs are just going to have a much higher chance of generating specular reflections.
Pfalz D.III/D.IIIa are by far the most common aluminum-doped aircraft though, and their ribs are only noticeable on the leading edges.