Speaking from past and personal experience, I find I have better losses with the red plan. I do try to have a couple of green days here and there but my body will not lose weight eating pasta and the like. Im sure others will have the opposite opinion, I think a mix of both is best.
Yes I think it's good to have variety in your diet, but I generally have red days simply because a) I can never think of anything interesting to do with potatoes and pasta and b) often I get TOO full up on a Green day and feel all bloated.
I find it easier to think of things to eat on a green day but have a mixture of both. I tend to feel full and bloated on a green day. But its nice to have the choice and i guess it keeps me fromjust living on pasta & jacket potatoes (tempting with being on somewhat of a tight budget!).