Airlines wet lease aircraft all the time (wet lease being a lease that includes crew, maintenance, pilots, etc versus a dry lease which is aircraft only). If the lease is long term, then often the plane is painted to match the leasing airline’s look and flight crews are provided with uniforms. But if the lease is short term, say filling the need for an increase in flights during a certain season or perhaps a delay in delivery of a new aircraft, then the aircraft may not be repainted.
Credit:stackoverflow.com‘