Fry the bacon with the onion in a large skillet over medium heat until the bacon is crisp, about 10 minutes. Stir in the chopped collard greens, sprinkle with salt, black pepper, and 1/2 teaspoon of the greens seasoning; cook and stir for 5 minutes.
Add in the darker chopped cabbage leaves, and cook and stir until almost tender, about 5 minutes. Stir in the remaining cabbage; season with salt, black pepper, sugar, and the remaining greens seasoning. Stir well; cover and cook until tender, stirring occasionally so that the greens do not scorch, about 10 minutes.