For my extended drain, I want to drain based on color rather than mileage. But in no way I am going over 6000 miles no matter what. So if it get too dark at 5000, I will drain it. Say I check my oil at every fill up. What color should it look like before I should actually change it. From the colors I would guess "yellow let it mellow", "brown it ain't down", and "black give it the smack!"