I prefer white or clear bottles so I can see if mold is growing in. And if that happens I just throw them out. Even if I would clean them and not see the mold I would still know it's there somewhere with my water, which I am drinking .... grosssss. I am not risking getting sick for a bottle which only costs 3 dollars at the first bikeshop.

And beside that, in due time the outside gets ugly from those scratches left in the plastic by the bottleholder and then the dirt get in those scratches.