If you'll allow an answer from a non-CBD dresser, I've been getting collars/cuffs on my bespoke shirts replaced when they fray. If the cloth hasn't faded signficantly - not typically a problem, though I just let the shirtmaker decide on this - I get them replaced in the same fabric. If it's an issue (or if I just want variety/a different look), I get them replaced in white (especially if I already have multiple solids in the same colour anyway). It's certainly cheaper than buying a new shirt, and also an opportunity to switch fastening style if you want. For example, l had couple of shirts changed from french cuffs to button cuffs, to add to their versatilty (it lets me wear them with sweaters).
I absolutely expected this to be the case in a non-CBD environment.
I'm having a hard time discerning whether replacing collars / cuffs on a non-white shirt with white makes it casual. Royalty would spare no expense and replace the entire shirt. If that is the case, I think I'll be building iteration 2.0 with business casual in mind.
Will at ASW just posted an article about the formality of patterned contrast-collar shirts. I posted a discussion thread here about their place in general some months ago, if you do a search.
I suspect the general cultural consensus (probably the most important thing from a CBD perspective, I would guess) is that a contrast-collar (solid) shirt is pretty much business-only, and you have to be very careful indeed not to let it become cheesy (and/or ironic). Think whatshisname in Office Space, or the 1980s-Guy in Futurama. I agree with Will that patterned contrast shirts drop down a formality notch. Recently, contrast shirts have been used in some casualish fashiony looks (I want to say RL or Hackett? Can't remember)
I have no idea what the royalty might do, or not do. :)
Sorry not to be more helpful; hopefully a more CBD-aware poster will come along soon and answer better.