They don't have to be solid green but they need to be firm.
You wouldn't want to fry them up when they were dark green and hard as a brick and at the same time you wouldn't want a tomato that was too ripe as it would fall apart.
I like a nice heavy cast iron skillet.
I then heat up some canola oil nice and hot.
Egg wash, then the flour and finish with the corn meal.
Mmmm the best thang to come from the south..Green fried tomatoes.