I'm not sure what's so absurd about this topic. I haven't played in any major tournaments before so I was just curious why card marking wasn't explicitly prohibited.
The topic is not absurd, for me its what people are saying with no citation in the rules. And in true internet fasion I will not give a citation either. I will leave it to say that I believe that if you sleve your command deck in red for Sith and black for Imperial Navy you are marking your cards. You are giving yourself the advantage of knowing beforehand whether or not you have a resource match. So while it does not technically sleeves must be uniform, I would interpert uniformity to be in the "spirit" of the rule.