After reading more posts from back in July, there's a third explanation that I think makes a lot of sense: The disc is in fact tinted green, but the differences in what people report could be due to how different people perceive color. Some people see color in absolute values, so they see the green. Other people, their brains interpret colors in relative to the color of everything else in a scene, so the green gets filtered out. Both of these approaches to perceiving color have their advantages evolutionarily speaking, so I think it makes sense that there would be these differences spread out in the population.
Under this scenario basically both parties are right. Those who say they don't see the green are correct, they in fact don't see the green because their brain filters it out. Those who say the disc is green are also right, because it is in fact green.