I found the info on Powerflex stiffness, that explains why everyone seems to be using Purple:Let me check my spreadsheet.....They were PowerFlex from 9/2004 purchased through BimmerZone
Red 65A – Used for our Universal exhaust mounts and diesel engine mounts.
Yellow 70A – Mainly used for engine mounts, diff mounts and subframe mounts or areas where the bush needs a lot of movement and absorption.
Purple 80A – Our most common material. This is used in most areas of the suspension and provides the right mix between performance and compliance.
Black 95A – Our hardest material. This is used for our Black Series range or on normal road vehicles where the vehicles suspension demands require us to use this hardness of material i.e. in areas of high load.