Pearlescent can be more difficult to match - based upon my late night viewings of dodgy TV like Boyd Coddington's Hot Rod Shop, Wrecks to Riches, etc.
I recall a car was resprayed in pearl blue - the front wings were sprayed separately to the car but during the same session. The wings had been stood/hung at an angle other than the final angle they would sit at when fitted to the car.
Result? Wings appeared to be a different colour when fitted.