Thanks everyone! Those psychodelic shorts are something else! haha...

Well, ideally I would like my shorts to be pristine white, but I also understood when buying them they were bound to get dirty at some point (they are just so pretty!). Luckily Assos thinks of almost everything, and they did make the back panel black, so at least it doesn't look like I crapped my spandex!

I think I will start by contacting Assos and see what they say (good recommendation!). And if that doesn't work, I'll start with the less abrasive club soda and work towards bleach. That does scare me with this fabric. I suppose I could try it first in a fairly hidden spot to see what happens.