I only have a casual collection of these advertising displays, cartridge boards, bullet boards, etc., picked up only because of availability at the time and when I had a few extra bucks in my “hobby money.” I do not seek them out. The only regular Thompson Center “wheel” that I have is Edition No. 5, but it, too, has a nickel .357 Magnum round on it. While these displays are certainly made to be attractive, so as to catch the eye, they also are educational and, once again, to show the .357 with a plain brass case would not be showing the norm for the cartridge. The educational value should and does outweight the cosmetic value of the item.
The only “wheel” I have seen (that I recall) that shows the .357 magnum with a plain brass case is actually a TC counter barrel display, where the upright portion has a printed version of the cartridge wheel, rather than actual cartridges. To add a color to that printing for one cartridge would not have been practical, especially on a display meant to hold various TC Contender barrels, resting in front of the printed wheel, and therefore when full, partially obscuring it.
I believe that using the nickel-case .357 on the regular wheels was not only practical, but also technically the correct approach. JMHO