Short Version: I want to be able to tell single.php which archive page sent the user to it.
Long Version:
I have posts that have multiple categories. So, perhaps my "All Things Orange" post belongs to the "Colors" category and the "Fruits" category.
If the user comes to the single "All Things Orange" page from one of the category archive pages, I want to be able to give the user a list of other similar posts based on the category. So, if the user came from the "Fruits" category page, I want to be able to produce a list of posts in the "Fruits" category, and not posts from the "Colors" category.
I thought this would be simple, but despite all my Google kung-fu, I can't figure it out. Any ideas?
Thanks in advance for any help you might give.