In a follow up to a possible delay of the SGS3 an anonymous source has revealed that Samsung is delaying the Pebble Blue Galaxy S3 unit due to issues regarding a manufacturing error. Specifically the blue shades on the front and back panels of the S3 don't match up, and the discovery was made only after the units were already shipped to the retailers. Samsung's official statement, however, is a little more vague but they at least addressed the issue:

Samsung’s Galaxy SIII Pebble Blue version comes with a newly invented blue colour and special hyper-glaze material. In order to meet the highest internal quality standards and to provide the best quality Galaxy SIII to customers, a short supply of Pebble Blue version is expected in some regions in the next 2-3 weeks. Samsung is working hard to ensure that customers will get the Pebble Blue colored devices as soon as possible.
So if you have your mind set on the pebble blue you will have to wait a little bit longer to get your hands on this stellar piece of hardware.

Source: S3 Forums