There is a consensus, or was a consensus, that jackets should be darker than the trousers. Also that shoes should be darker than trousers. Very dark casual pants (navy, black) don't work in a wardrobe built around those principles. A lot of standard jackets (gray herringbone, navy blazer) and standard shoes (dark brown) don't work with those principles and navy trousers. Pretty much the *only* trousers that do not work with the navy blazer, which has long been the definition of the versatile jacket, are navy and black. So you have to reinvent all the older ideas, go against the grain, etc., to make navy trousers work since most age-old staples of menswear are not going to work easily with navy trousers. Also navy pants are for gas station attendants. Just kidding. Thought I'd slip that in to see if you are paying attention. These days navy and pants are very common, not so much with jacket and tie but with polos and button-down shirts and sweaters. But, I know a number of men who wear no tie and a gray jacket with navy chinos or navy wool pants (that are probably half of a suit). This looks pretty 50ish & 60ish to me, as I only see older men "rocking" this look. What shoes are you going to wear with navy trousers? Maybe the right brown. Black? I like the darkest thing on me to be my tie or my jacket or my glasses -- something that anchors the eye near my face. Dark denim is navy, but this has such as characteristic texture, it works in ways that navy chinos or navy wool pants won't. And it almost always looks better without some kind of sports coat. If I was stuck with only navy pants I would probably start looking at outfits that work with dark jeans and try to get that to work. Maybe a dark charcoal plaid jacket, or a dark brown corduroy.