Many people claim to have seen or even been abducted by aliens. Many times, the description of the creatures that they encounters are Greys. In Starfinder, these Greys also exist and they're part of the group The Unseen. Not much is known about them (for obvious reasons), but Paizo's taking a look into them, hopefully to spread more information about just what these creatures are up to.
From the post:
The Threefold Conspiracy Adventure Path has begun and I have uncovered additional resources for Starfinder mystery and conspiracy adventures!
The Unseen are mysterious groups that infiltrate various organizations for their own gain. The only documentation that has been widely distributed can be found on page 497 of the Starfinder Core Rulebook and the Zeffrac Science Platform entry on page 116 of Starfinder Pact Worlds. For speculation, watch Who are The Unseen, Starfinder Lore - Starfinder Wednesday with Starfinder Developer Jason Keeley and Starfinder Creative Director Robert G. McCreary, who some claim are authorities. Note: spoilers for The Threefold Conspiracy Adventure Path were avoided, but GMs may wish to preview it for their players.