This is an excellent post, detailed but focused and not at all rambly (the way mine sometimes turn out).

What struck me most was thinking about color vision. In these particular photos, the differences between yellow and brown were pretty obvious (to me), but someone who has difficulty on the red-green axis might have a very different view. One way to check would be to upload these photos to http://www.vischeck.com/examples/ and see if they get harder to distinguish.