There is I find so polished and flattering when using a monochromatic ensemble. A set of pants, jacket and shirt in the same color gives me 100% a vibe of chic and cool.
If the shades of choice are dark ones, the outfit would not only be perfect for both day and night, but it will create an slimming effect, and it can be magnified by the usage of a pair of stilettos. Use accessories to break the monotony of the look (enough blue for me, I don´t want to look like a Pitufo).
You can shop a coordinate of pants and jacket and then add a shirt in a similar shade, or you can do like me, and use three separates and match them together. I don´t think the three pieces have to be the same exact shade.
Believe me, although you think there is only one shade of blue marine, it is not true! There are hundreds of shades for the same color, so don´t break your head trying to find the same exact shade. I like the monochrome look, with a little imperfection on it.