Version number 5 is an oil-fired locomotive in the classic two-tone gray livery utilized by the Union Pacific for passenger service. The original construction was that of coal-fired locos which were converted by the railroad. Often referred to as the 'Greyhound' paint scheme, there were two variations used by the road, but only the earlier of the two were ever applied to the Challenger class locomotives. The early paint scheme as shown above featured silver-gray accent stripes outlined by black adjacent to the dark gray broad stripe on the tender. The later scheme replaced the silver-gray stripes with Armor Yellow also eliminating the black accents. The early paint scheme was meant to match the Pullman cars used country-wide that commonly had the two-tone gray paint scheme. The later arrangement was meant to better match the streamlined cars used by the road, but the Challengers were withdrawn from passenger service prior to the change order being applied to the class..