550: Significance of red and black key fob/remote?

I got multiple sets of keys for my 550, and each key comes with a red and black key fob/remote. The manual states that they are “master” and “slave” remotes, and that I should lend out the black one if needed but never the red one, but what is the functional difference between the two? Are they just spares?

 

That’s the manual I read. I don’t know if I’m missing anything, but it basically states that there are red and black remotes, but not how they’re different.

As far as I can tell, they’re identical. Maybe one is colored red so that owners think of it as “the spare” and keep it separate from the remotes that are used every day.