This couldn’t be more timely for myself.
In my post from little over a week ago I was asking for just this sort of discussion. Although by “contrast” I was talking about color contrast whereas this article is about all different manner of contrast such as contrasting size, shape, orientation, and so on.
But the real gem of this comes in the comments on the article in which this pdf: Essential Web Skills is linked. This appears to be a PowerPoint presentation that’s been converted to PDF. We don’t have the audio of the presentation, but there is still quite a lot here that you will get something out of it anyways. Especially interesting is page 40 (as noted by the ALA commenter) which talks about text as not just content but also as the user interface.
It’s interesting stuff and worth a peek.