To the best of my knowledge Squiffy the difference in color (colour!) is the result of different panels, fading, weathering, etc. I forget which Windsock has an article on these hangers (with plans!) but Ray R. included some color shots of one of the last ones still in use. The images showed various fading, etc. like you'd expect on tent canvas left out for a long time, etc.
Now, I'm not saying they weren't camo'd, as I honestly don't know one way of the other, but I'd go with fading, etc. first.
That's just me however.
HTH!
Warren