In 2017, when I flew down to the uncontrolled Converse County Airport, near Douglas Wyoming, to view the total solar eclipse, a couple of hundred aircraft arrived in the morning or the day before and then departed in the afternoon.
Call signs were very pragmatic - nobody used their registration - it was "Red High Wing", "Blue Low Wing", "Green and White Twin", etc. and it all worked very efficiently.
We are lucky that our aircraft is a very "distinctive" colour, but all the Cessna's and Cherokee's based at our airfield are mainly white overall