I believe that the easiest way to differentiate them is to check the newly hatched poult color. http://www.porterturkeys.com/lilac.htm http://www.porterturkeys.com/variouscolorcombos.htm I suspect that a self blue rusty slate would have a newly hatched poult that is a lighter version of the rusty slate poult. I also think that the tail feathers of a lilac are not as dark as those of a rusty slate but your question is best answered by Mr. Porter. There is a contact button on the main page. They also have a turkey genetic group that is good at these answers.