The color of each tile represents the brand color chosen by Microsoft for that product or application. The tile colors are not related in any way and do not indicate any connection or relationship between tiles unless one is explicitly set. We're just following Microsoft's lead here.
The color of each grouping title and line are arbitrarily chosen in a way similar to how countries are colored on a map. Light in nature, unassuming, easy to tell the difference, and not distracting from the actual content.