I agree with GinaGt. Abnormal barking could present a whole host of medical problems, most commonly, cataracts. A dog with bad eyesight or aging eyes often bark at their people just because their people are wearing odd-colored shirts or hats.

Also wanted to add you can do an impromptu home eye test by taking a non-scented ball and moving it slowly in front of your dog's eyes. They should follow the ball, but you have to remember that dog's use their noses to sense objects as well. Also, you can take your hand and slowly push it towards Blair's eyes. They should close, a natural reflex. If his reactions are slower than normal, vet ASAP.