As the title suggests, how does one make sense of the colour code displayed on the card in your engine bay (or wherever)? E.g. my car's colour is 51E. Another one of my cars had colour code 3KU. How would a paint supplier know that 51E is white and 3KU is a metallic grey? And can you tell from just the code how to mix the paint, or do you need to look up the "recipe" from a universal lookup resource?