Found your blog post while looking for an article to your very question. I found it, and thought you might want to read it. It is just the summary article, not super in depth, but based on actual scientific research which is cited in the article, and that full research can also be found online it seems.
NF91-44 Ineffectiveness of Home Remedy Dye Setting Treatments
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2440&context=extensionhist