Just got back from a road trip with my diesel truck. I noticed at the different stations where I filled, that sometimes the fuel is a greenish color and gets foamy when you fill. And sometimes it is almost a clear color and not hardly foamy at all. What is the difference if any? I don't know if the mileage was better or worse on either one. I was getting good mileage on the last tank that was the clear stuff until I hit that cold front with the strong head winds that came through and it really went down. My son was also driving with his and the computer mileage was showing 21 till he hit the wind and it went to 15.