Cameras pick up color in different ways. Remember that the prototype has also been out in the sun and weather.
From NS Heritage page, the Lackawanna "rolled out" June 27, 1999.
"Since the 1820s, hundreds of railroad companies were built, merged, reorganized, and consolidated into what eventually became Norfolk Southern, itself created from the consolidation of Southern Railway (SR) and Norfolk and Western Railway (NW) in 1982. In 1999, Norfolk Southern expanded the scope of its heritage with its acquisition of a portion of Conrail (CR). The heritage locomotives represent most of the railroads that played significant roles in Norfolk Southern’s history. The first unit, Conrail 8098, rolled out of Altoona, Pa., March 15, and the final one, Lackawanna 1074, rolled out of Muncie, Ind., on June 27."
Take a photo of yours outside or a bright sunny, clear day and compare. The Floquil PollyScale colors are another way to compare.
The yellow on the MTH looks a little brighter comparing the photos that you posted. Could be weathering. I am sure that NS or historical records would give a licensed modeler the color numbers or specifications. You have a fresh paint job.
What stands out to me is the Lackawanna on the MTH is not as bold and smaller.
It's a nice looking engine and very close in color.(again, by the photos)
It's what you think and like. If it really bothers you, return it. Perhaps try to see another in person. The mfg. paint could vary from batch to batch.