Wagon wheels look very nice indeed. The single wheel method on Bachmann axle is very clever and saves the real problem of removing metal from the triang castings, the coach bogies need alot of metal removed. However for wagons it is a bit easier and the wheels pretty much drop in.
My guess withe the blue grey is it was a period mod, who knows what excess new stock was selling for at the end of production, probably at giveaway prices.