I believe older EMD units could display green and white classification signals. I seem to recall seeing F-unts showing white lights usually, for extras, which almost all freights on most roads despite symbol schedule.
I do recall when waiting for school bus [about 1963] seeing a PRR on the E&P in Jamestown PA displaying green for following section and about ten minutes second train came through showing the usual white signals. I know they were probably both extras since there was no tt authority [MBS using Block Limits], but they may have done it to attract attention so no one [such as mofw] would get onto track until both trains cleared.
Did see plenty of use of those red lights on rear unit whether pushing or running light on F-units to SD units.