The question is, why would the green light of kryptonite hurt Superman? Obviously the red sun of Krypton would emit less green light than the Sun. The Sun's light curve peaks in green light, but Krypton's sun would peak in red and infrared light. Still, even Krypton's sun would emit some green light. So why would green light hurt Superman so badly? Any theories?
According to Superman: The Ultimate Guide to the Man of Steel it's the radiation emitted by Kryptonite that is harmful to Superman. It has nothing to do with the colour of the light that it emits. Kyrptonite radiation seeping through from Krypton's core was responsible for the planet's demise.
