2. The Lighter Look
The one thing about every Doctor so far is that they all have a 'heavy' look to them. Every one of them has some sort of jacket they wear over the rest of their clothes. Maybe Capaldi's Doctor can be known for being the first to completely lack it. You could talk about how cold it can be during filming hours which is a fair point. But even when they wore heavy coats like Tennant the actors still wore extra coats on top to keep warm between takes. So I see no problem with Capaldi wearing a little less. Plus, he's Scottish like myself, he's probably used to some colder weather. Perhaps I should actually talk about the outfit though. It'd be simple. Light. A waistcoat. Small scarf for decoration. And glasses. If he's going for the light look I think he'd definitely need glasses. Not only because he suits them, but also because there'd need to be a main feature to attract the eye. Plus he'd be the first Doctor to wear 24/7 glasses, not use them simply as brainy specs.