How do i find a distinct group of Product attribute names? ie browse by colour menu!

Hi guys,
on the left hand side of my page I would always like to have a "shop by colour" feature..

So what i'd like to do is query all the products who have an attribute of colour defined and then get a distinct of the colour names..

I was just wondering how i'd go about doing that? Im very used to linq-to-sql and it appears nop isn't using that and would love some hints on the api!

Cheers,
Tom