Why was this Gen Set painted dark grey?

A friend of mine just bought a Cat 46-30 S Gen Set and we noticed you coul still see the original decals under the paint so we scraped off the new paint down to the original paint and decals. What we found was dark grey paint behind the decals not old Cat yellow. The serial number on the D4600 engine is 1S5012 so it should have been made in 1945-46. Could it have been a military stand by or what? I've never seen one painted any color but yellow. I know for a fact that it was originally dark grey but why?

Thanks for any help, Josh.

Think you answered your question.....most likely a military spec...probably Navy where everything is either Battleship Gray or Haze Gray.

haze gray and underway! US Navy, look for some chrome parts that some sailors may have spiff'ed up. i've got close to dozen pieces that were plated on my 38-d13000 navy genset. mine came out of lancaster pa. area (bird in hand). look for navy tags and stampings. good luck.