The people in the academy's, that have the missions to get more white doffs, also have a mission to exchange 5 white for 1 green or 5 green for 1 blue or 5 blue for 1 purple (With a small chance to get a v.rare now)
Those "people" are identified as "Personnel Officers." There's a generic Starfleet one in the library with Lt. Ferra, there's a Tellarite and an Andorian arguing out behind the library, and there's a Vulcan staring at a signpost to the south.
The Starfleet one also offers the old "Cadre" assignments, i.e. get a 2-3 doffs in specific departments (Tactical/Security, Engineering/Operations, Science/Medical, or Civilian). The other 3 offer "Cultural Exchange" assignments to get 1 doff of their species.