In later years, Santa Fe adapted the scheme to its gas-electric "doodlebug" units. The standard for all of Santa Fe's passenger locomotives, the "Warbonnet" is considered by many to be the most recognized corporate logo in the railroad industry. Early after Amtrak's inception in 1971, Santa Fe embarked on a program to paint over the red bonnet on its F units that were still engaged in hauling passenger consists with yellow (also called "Yellowbonnets") or dark blue (nicknamed "Bluebonnets"), as it no longer wanted to project the image of a passenger carrier.