Yes, SW does say that you can eat unlimited amounts of free foods, what you say about your tuna meal is not excessive. I can easily eat that! I can certainly eat a lot!
I did find, but is is just me and I can't speak for everyone, that to lose weight I cannot eat a lot of mullers or fruit. Particularly grapes and bananas. Even though we don't count calories, they do have them so a lot of them don't work for me.
I don't think you need to change to red unless you want to. I eat a lot of meat, but I also like my carbs, so EE is the only plan that really works for me. I have done SW several times. This is my 6th time and I failed because red and green doesn't work for me as I want both at the same time!
I do think that you need to have the 1/3 superfree foods with your meals, and also eat until you are just full, and not really stuffed. Also eat when you are genuinely hungry, and not for the sake of eating.
This has all really worked for me, and I will continue with it for life!
Good luck hun!