Steve,
Here is my 2011. The cast cap dates to the 1928-34 time frame according to Alan Schuweiler's Guide to AF Wide Gauge. No light on the 2011, lenses are red (mine's faded to an orange), green, and white (clear), possibly this had been yellow at one time and faded like the red . Pre '28s had a brass cap in place of the finial. I don't own a 2018. Never thought they looked much like RR signals.