Shampoo is (virtually) always clear – conditioner is (virtually) always cloudy/opaque.
I’m guessing that, at least originally, this was about the different kinds of ingredients in the two products. At this point, however, I’m guessing manufacturers could come up with a clear conditioner if they wanted to.
Is this about either a) customer convenience [you can tell which bottle you’ve got at a glance], or b) customer expectations [you wouldn’t expect conditioner to “do the job” if it were clear]?
This is pretty mundane and stupid – mods, feel free to move it…
But I’m curious.