Harp stand (D&RGW) target colours

Is there a chronology or other taxonomy to the colours used on D&RGW harp stand targets?

Most people seem to use the red/white vertical split style on restorations, models, etc. However, if you look at Bob Richardson's collection:


[digital.denverlibrary.org]

3 are identifiable as solid light-coloured (yellow or white?), 2 as split-light/dark (presumably red and white), and roughly 6 are either dark or indistinct.

Now some (or even all) of the dark ones could be red/white with all the paint rusted off, but it seems more likely that at least some of them are solid red. And either way, that can't explain the solid-light coloured ones.

So is there a rhyme or reason to what was used where?

(And are the light-coloured ones white or yellow?)

Cheers,
Jeff.