The logic there is that Dooku would be the first Jedi we see with a Green saber, so it's more ambiguous. One could say he could be seen to be walking the grey path rather than the narrow and dogmatic way of the Jedi or the oppression and subjugation of the sith.

Then when we see Luke with a green saber too, we think back to dooku and how he failed and we wonder if Luke will succeed.

Nevertheless, I'm still not sure about what I'd prefer. I do like the idea of ROTJ being the first time we ever see a green saber though...