I think that was the canals...
Although one would think looking at a red planet with dark areas, you might be right. The eye "fatigues" on a color, and if you stare at something red for a long time, and then look at a colorless area, a green afterimage will appear (the complement of red.) I would not be surprised if dark gray areas on Mars would start to look "green" to a telescope observer.
But then, there were astronomical photographs, which don't have this optical effect. Was there any "green" on them?
Anyone have more information in this area?