Neutral is key here. Navy is the most common, but a black or understated gray can be equally as versatile. The blazer is great because it adds a formal look to an outfit without making you look overdressed, and you can pair it with many different shirt/pants/tie (if necessary) combinations. Dress up jeans with a blazer, or throw one over a shirt and dress pants for an after-work formal look. Wear it with your sockless shoe in the summer and layer it with a sweater and button down in the fall and winter (see this impeccably done above). The possibilities are literally endless. I'm partial to the traditional navy blazer, but just make sure you get a color that works best with your wardrobe and a fit that makes you carry off this look convincingly. Once you add this item to your closet, you probably will wonder what you did before you had it.