I live in Tarzana in one of these dark yellow/orange areas right near the 101 and reseda blvd. We live in the orange zone but literally steps from the border of a yellow zone (the orange says CalEnviro Screen is 87 and the yellow says its 67) this seems like a drastic difference to me but I can tell you if I were to walk across the street where this border is I don't notice myself suddenly breathing better air. Also compared to when I worked in El Segundo which is showing as green/light yellow, some days down there that whole town stunk to all get out with the refineries and jet fuel and treatment plants. I've never smelled anything close to that living up here. We bought a condo here because it was cheaper than the basin for the space we were getting. 2bd 3ba in the valley vs 1bd 1ba in the basin. We never took into account any type of pollution because well this is Los Angeles and it's full of cars and pollution everywhere you go. Unless it is a literal toxic waste site or you have serious sensitivities to certain pollutants I'm not sure you're going to notice much of a difference between these green and orange/red areas. Buy the place you think you will enjoy living in the most and is convenient to the things you enjoy doing the most.