Put the colours side by side
The old idea that navy and black should never meet is not a useful rule for getting dressed. What matters is the particular blue, the particular black and the amount of each that you see. A deep inky navy can look almost black indoors, while a brighter navy makes a clearer contrast.
Check the pieces in daylight and again in an ordinary room. If the near match looks accidental to you, create a stronger difference in texture or in the area covered by each colour. A navy knit above black trousers is easier to read than two nearly identical smooth jacket fabrics placed together.
Let texture do some of the work
A ribbed navy jumper beside smooth black trousers has a visible distinction even when the colours are close. A matte black skirt and a slightly lustrous navy blouse offer another contrast. You do not need to add a third colour merely to explain the combination.
If the outfit feels too flat, try changing one fabric before changing the colours. The problem may be that every surface absorbs light in the same way. A different shoe finish or a more textured bag can make enough difference without turning the outfit into a collection of competing details.
Choose where the colours appear
A large navy coat over black clothes creates a simple outer frame. A small navy scarf against a black top is more subtle. Both can work, but they produce different results. Stand far enough from the mirror to see the blocks of colour rather than inspecting each item separately.
A white collar or pale shoe can break up the darker areas if you want more contrast. Keep it because you like what it does, not because the outfit needs permission to contain blue and black. Jewellery can remain as simple as it would in any other combination.
Check the small near matches
Belts, shoes and bags do not all need to be the same shade. However, if several slightly different dark colours bother you, simplify one area. A black shoe and bag can give the accessories a clear relationship while the navy stays in the clothing.
Wear the combination for the setting you intended. An outfit that looks subtle in daylight may appear almost entirely black in a dim room. That is not necessarily a problem; it is just useful to know. Once you stop treating the two colours as a forbidden pairing, the decision becomes the ordinary one of whether you like the fabrics and proportions together.
