Blue bags suit anyone who's tired of their accessories doing nothing but matching black trousers and staying silent. If you want a bag that quietly lifts a plain jumper and jeans without you having to think about it, this is the colour that does it. Think twice if you're someone who buys one bag a decade and needs it to go with absolutely everything without a second thought, because navy is forgiving but a bright cobalt or a pale denim blue will ask a bit more of the rest of what you're wearing.
Before you buy, look properly at the hardware, not just the colour swatch on the screen. Gold fittings on a mid blue can look wonderful or slightly cheap depending on the finish, so check whether the metal is a flat gold or a shinier brass look, because the brassy kind tends to show wear fastest. Check the lining colour too, a lot of blue bags are lined in black or grey, which hides marks, and a few are lined in cream, which will show every biro and every receipt within a month. Feel the strap drop and imagine it over a coat, not just a t-shirt, since blue bags often get worn through fatter months when you need another few centimetres of strap. As for what it pairs with, a navy bag goes with almost the same things black does, grey, cream, denim, camel coats, without looking quite so flat next to them. A brighter blue works best against neutrals, white shirts, beige trousers, a grey coat, where it gets to be the one bit of colour rather than fighting another bright piece. I'd avoid putting a strong blue bag next to green or purple unless you've genuinely thought about it, because that combination can tip into looking accidental rather than chosen.
Over time, blue is one of the kinder colours for ageing well, especially a darker navy, because scuffs and scratches don't show up as starkly as they do on black or tan. Lighter blues will pick up colour transfer from dark denim, so wipe the base occasionally with a dry cloth if you're wearing it against jeans a lot. Keep it stuffed with something when you're not using it so it doesn't go slack at the sides, and store it somewhere it won't fade, blue is more prone to sun bleaching than people expect. A good one, cared for like that, will still look sharp years on. And there's a particular pleasure in a blue bag that's broken in just enough that the corners have softened but the colour hasn't dulled, the kind you reach for without checking what else you're wearing first.