I won't discuss against two supreme experts, but I'd like to say that i think it's a not-so-good idea to look directly into the sun when it's high up in the sky. Just believe me and don't do it again!
Maybe I should get that book, and somewhen I might come up here with a few thoughts about it.
BTW, IIRC the reason for the green afterimage is that when all types of cones are "overloaded", our brain interpretes the resulting equal "firing" of the nerve cells as green image. Remember, we actually have no sensors for the green light, this colour is interpolated from the values for blue and orange.