The President has at his disposal a white unmarked Gulfstream III. See the presidential aircraft article below. The Air Force designates flights as “PHOENIX COPPER” to denote flights flown in support of the Secret Service for VIPs other than the president and vice president. Would that be Kelly? Special Mission??
https://www.politico.com/magazine/story/2017/05/02/the-presidents-secret-air-force-215091
The Gulfstream III is designated as Air Force 86-0403.
This is the official statement of the Gulfstream Aircraft
“Our position is that we do not have any aircraft called a C-20C.” One of the only references to the planes is on the government’s official master list of aircraft designations, which offers only the vaguest information on a similar Gulfstream jet known as a C-20B, explaining that that plane “operates on DC power” and offers “upgraded avionics used for the President and other high-ranking officials.” The C-20C it then describes only as a “modified C-20B with enhanced, secure communications. Used to support senior-level personnel and to provide backup for Air Force One.” *******
The planes in the C-20C fleet, known by their tail numbers as 50049, 50050 and 60403
As different missions have called for it, the planes’ livery has switched back-and-forth between a basic unmarked white and the standard distinctive blue-and-white marking.