Many of the different shades of color are just the result of the manufacturing process. For example, you will find Quatchi in many shades of brown.
There are 3 different Royal Mint pins that were handed out during the Olympics at the display. There is also an internal Royal Mint pin that was never handed out or for sale.
The one pin in which there are 2 legitimate different colors is the Umbrella #1157. It was originally released in a light blue - almost a light grey. Artiss Aminco, the manufacturer, did not like it so changed it to a dark blue which is the more common version.