color coding on the valves for bmw I'm not sure of their exact specs or reasons for each color but typically valve springs are color coded according to installed pressure to keep the spring pressures approx. the same on the head, the factory doesn't usually shim to set spring pressures so the color coding allows the assy line workers to match pressures on a head.. Some manufacturers also put the paint mark at the top of the valve spring to indicate which side is up when installed, some progressive wound and non progressive wound are marked this way. And some manufacturers use a different color code not only for the spring pressure and free length but also to indicate the alloy used on that particular valve spring.
Originally Posted by Hector