Once again, never say "never" or "always". Then I go ahead and violate my own rule!
I can only say that I saw freights in action in the '60s and didn't see the white paint. From seeing the C&TS and your operation at Georgetown (a class act, I might add) the white stripes are VERY noticeable and not something you could miss.
Also, I just got through going through Narrow Gauge Pictorial Vol III, Gondolas, Boxcars and Flatcars of the D&RGW. Lots of photos of hi-side cars taken in '67, '68, '69 and some '70. Not one single photo of a car with a white striped wheel. Maybe they existed on the Grande, but not so you'd notice.