Dav is right about the bright orange cagoules (and tents) that were once seen all over the hills, for the very reason gld mentions. But some people, including at least one guide book writer (sorry, I can't remember who) found this an eyesore, and there followed a trend towards more subdued colours. Anyone wanting to combine wildlife observation with mountaineering may prefer more camouflaged clothing too; You're unlikely to see Bear Grylls on the mountains in day-glo orange!
A friend and I encountered a particular guide on Aonach Eagach, better not say who she was (errr...not saying whether the previous posts give a hint) and wouldn't have her guide me if she paid me. In fact dav, this was your reply to my friend's report of that day! Copied and pasted, don't know if you remember...
[Well done indeed!
That was a totally absorbing report to read. Cracking photos too - some of them quite stunning. Surprising that some of the parties you encountered were roped up; that seems well OTT for a summer traverse (Winter a different matter). That guide sounded positively rude!]
However, I agree safety is paramount. I personally prefer blue clothing on the hills, which I feel gives a reasonable compromise between visual pollution and invisibility. My emergency survival (bivvy) bag is orange, though!