Differences in Sandisk Memory Stick Pro Duo Colors

Believe it or not there are a few differences in color for SanDisk Memory Stick Pro Duos.

Black - Normal
Blue - Comes with a Duo adapter
Green and Yellow - Gaming


Also note that unlike other cards (SDHC, microSDHC, ect.) Memory Stick Pro Duos are NOT Class 2. IDK if it's because they are locked out of using it on a Memory Stick Pro Duo or what, because Sony makes a Mark 2 Memory Stick Pro Duo?

Just figured I'd let you know that Sony's Mark 2 is faster than SanDisk's Memory Stick Pro Duo. However all the other cards that have Class 2 have Sony beat.