This Christmas-morning frittata, in fitting with the season, is strung throughout with the green and red lights of spinach and tomato. Of course, you could make it any time of year. Of course, you could make a frittata with any combination of color (vegetable, flavoring, meat, leftover, and so on). That’s the idea of a frittata — to use up what’s there in one last fling on the stove. I’m always surprised to read that most frittata recipes bake the thing, when the name itself, I am pretty sure, doesn’t simply refer to using a frying pan just to house everything.