On that note, something I've been wondering about. AFAIK it's pretty much only Chabad where adults commonly wear yarmulkas in all colors and designs as opposed to plain black.
Is there a reasoning or minhag behind this, or is it simply a style/individualistic/random thing?
I don’t think it’s only Kippahs or only Chabad. Jewish communities where people were black and white, they also tend to wear black Kippahs, same for other communities where people dress in all colors of the rainbow, Kippahs included. In Chabad there are people of both persuasions, and then there are Chabad (or non-Chabad) people in the middle who wear dark pants and jacket and a white shirt on regular weekdays, but accessorize (ties, Sweaters, Kippahs, scarves, etc) in louder colors.