Green means you've received StreetPass data from passing players in sleep mode.
Blue means SpotPass data from Nintendo has been downloaded.
>StreetPass provides you with an amount of PokéMiles (PM) for each person you've met who is also playing a StreetPass enabled X or Y. PokéMiles can be traded in for items at the Lumiose City Pokémon Center. Alternatively, you can redeem them at the Pokémon Global Link website via the Game Sync feature of the PSS; the prices there are lower than in Lumiose, and the items you select will be delivered to the Pokémon Center of your choice. Eventually, you will be able to use your PokéMiles to play mini-games called "Attractions" on the Global Link website and win items, though at the time of this writing, no Attractions have been released yet.
Hopefully I've Helped!