I didn't know that too, i checked the one i have in my collection and it's different that the one on the picture, the blue is a bit darker, don't have the USK logo and the item number is just "SLES-52237" instead of the "SLES-52237-GER" i can see on the picture.
This is the one i have (thanks MobyGames):
The image you showed seems to be a German-only release (they often do that to censor games for Germany...
), are the two version that you have the same (with USK logo and "SLES-52237-GER") ? If they are not the same it would probably mean that the light blue was for the German release and the dark blue for the European release, and if they are the same... then i don't know
.