When a man, specifically a Greek man is eating a home cooked meal and says "Not bad."
What he really means is that the meal is to his liking and he is satisfied.
"How is the lasagna Doctor?" asked the Paki girl. With his lips full of tomatoe sauce the Doctor replies "Not bad."
A plate of brown consists of foods that have little to no nutritional value, and are typically deep fried. A true plate of brown will also be accompanied by a dark soda.