As I understand, after a major overhaul in 1983, the first Re 4/4Ii was painted in red livery. It was then decided that all post-war SBB engines would be switched to red in conjuction to these overhauls, however, there was to fixed timeline for this makeover.

For Era III until 1968, SBB locomotives were mainly olive green. There were some interesting test colours used on Re 4/4I in the 1950s. The Re 4/4II went into service in 1964 (11101-11106) with the rest of the series entering service starting in 1965 and the locomotives with 2 pantographs as of 1969. The TEE colours appeared in 1969 and the Swiss Express livery in 1974.

For Era III, the locomotives to look for would be the Ae 6/6(Maerklin/Piko/ESU), The Re 4/4II (Roco 2024) with one pantograph*, the Be 6/8III(Maerklin/Roco), Ae 4/7 (Piko) and Ae 3/6 (Maerklin/Roco). Piko has RBe 4/4 models available in Switzerland.

If you need more info on which models to look for, I will gladly help you, even though my collection and interest is 1968-the present.
If you want some consisting ideas, the book "Die Gotthardbahn" by Marti and Trueb can be found on eBay frequently. Look for the 1968 or 1971 editions.
You can also look at some nice classic photos here:
http://www.polier.ch/page/archiv/Sutter/Sutter.htm
https://bahnbilder-von-max.ch/sbb/index.html

When we were in Switzerland as kids in 1971/72, the TEE and BLS/SOB/BT trains were so cool with their unique colours

Regards

Mike C

Marklin did make several digital versions of the old Ae 6/6 model, including the 3650 and the recent 30501 double pack reissue (one green, one red). The red one obviously is not Era III.
In the early 1990s, they released an updated version of the Ae 6/6 which was more to scale and better detailed. Those locomotives were available in analog and digital. The green digital models were 3638 (Canton Berne), 3737 (City Basel) and 37366 (Lucerne). From what I recall, those models were in 1970s/1980s paint. There was also a green one in a set (29850) (Arth Goldau) also in late 70s markings. In earlier eras, there was the 37362 set which had a green one (Canton Schwyz). More recently there was the 39364 (Canton Aargau) and one from a set (29814) (Canton Baselland) as can be seen here: https://www.ebay.de/itm/355648671406? and another one from the 29680 Set (Canton Lucerne)

Other manufacturers have current models of the Ae 6/6, including Piko and ESU.

ESU 11401 (Ticino): https://eyro.ch/onlinesh...21&products_id=18122

Piko has some models of the following types: Ae 4/7, RBe4/4 and Re 4/4I https://eyro.ch/onlinesh...x.php?cPath=21_27_41_836

Roco has models of the Ae 3/6 (78088, etc) www.roco.cc

Maerklin had the RAm diesel in exact scale (39706)

You can also find BLS models for the 1960s too.

If you need any more help, feel free to ask.

Regards

Mike C