Regarding the color, if neon pink worked then stay with it. The color is there to get your attention and that seems to work, not sure why one wants something more "appropriate".
Duke - It could be my mistake, here is what I use:
37mm L/45, [TOAW III-D]
37mm L/45, [TOAW III-E]
50mm L/42, [TOAW III-F]
50mm L/42, [TOAW III-G]
50mm L/42, [TOAW III-H]
50mm L/60, [TOAW III-J]
The problem is simple that the PzIII is a mess regarding its armament, usually you would expect German equipment to be more orderly designated but that did not happen with the PzIII. The upgrade from a 3,7cm to a short 5cm and then a long 5cm did not go along the versions but it simply happened at a point in time in the production cycle of these many versions.
F production only received the short 5cm in the last 25% of its production while the G(that ran for some time parallel to the F) received it in the last 66% of its production. So there are F & G versions with the short 3,7 and that was the case at the start of Barbarossa. "Panzer Divisions - The Eastern Front 1941-43" by Pier Paolo Battistelli give some numbers and for the 22.06.1941 there were 259 PzIII with a 3,7 in the panzer divisions. 259 is more than the production run from the A to E version so it's clear that even a year after the Battle for France there seem to be F/G with the short 3,7cm gun.
That mess went on with the long 5cm but that isn't my scope here. I just note that the J version was produces since March 1941 but the long 5cm was not introduced before December 1941, so you will have short and long 5cm J versions at a certain point in time.
Hopefully Derek replies but if he wasn't around for 4 years I think that is unlikely.