Sure, you can be associated with a certain colour such that anyone else in your field who was using the same colour might be confused with your organisation, and the law might legitimately protect against the misrepresentation in that case.
IIRC, this is one of those legal issues where finding a case that actually went to court is quite difficult, because the major cases tend to settle instead, but perhaps there has been the occasional definitive ruling.
In any case, though, that is not what Royal Mail's wording used to say. They didn't claim, say, Pantone colour X. They claimed "red".
Contrary to urban myth, Royal Mail does not own the trademark on the colour red, but a specific shade of the colour red: "Royal Mail, the Royal Mail Cruciform, the colour red (as part of the Royal Mail logotype) and SmartStamp are all registered trademarks of Royal Mail Group plc."
Exactly. That's not what it used to say. I know that, because before I posted my original comment, I checked some printed matter from about three years ago, and the parenthesized part wasn't there.
IIRC, this is one of those legal issues where finding a case that actually went to court is quite difficult, because the major cases tend to settle instead, but perhaps there has been the occasional definitive ruling.
In any case, though, that is not what Royal Mail's wording used to say. They didn't claim, say, Pantone colour X. They claimed "red".