Maybe he is aging his hair in the style of the Barcodes colour scheme?
VIVAELCITIES
"The adjudicatory chamber of the Ethics Committee ... has banned Mr Joseph S. Blatter ... for eight years and Mr Michel Platini ... for eight years from all football-related activities (administrative, sports or any other) on a national and international level. The bans come into force immediately." - 21/12/2015
I reckon its a salute to the toonarmy, no messing.
I even think he shaved/trimed one of his eyebrows to give the total half and half look. The fans love him and rightly so. If this is the case, imagine what it would be like to have your manager embed himself in the club like that? I love the way Bobby wears the city scarf, so I can only imagine if he was over achieving with us and dying his hair blue!