When navy looks black...
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If your suit has a local color that has a blue in it, it will always show the blue. How much blue you will see depends on the color temperature of the light. Under a strong white light (the sun on a clear day between 11:00 and 13:00), or a light with a cool color spectrum (your average office ceiling light) you will see blue. When the light becomes warmer, the midnight blue will absorb more of the light instead of reflect. Making your suit black, most often blacker then black suits. Black suits tend to be dyed with a warm paint, so they work better at night.
What does that mean for shoes? You need to vary your shoes based on where you are going to be. Going out at night, you need black shoes (any warm tinted shoes will reflect more of the lights and become an eyesore) When going to an office or outside during the day: warm colored shoes, that share the same value as the suit.