Which color of shirt is most appropriate for a bluish-black suit?
By a bluish black suit, I’m going to assume you are referring to midnight blue; a blue so dark as to appear black. It is used to great effect for tuxedos (as seen here on Jeremy Renner), as it can appear blacker than black in certain light.
If you’re talking about a tux, I recommend sticking with a white shirt, but if you’re talking about a suit, the world is your oyster. White will always serve you well, but do not be afraid of a light gray, or a medium or light blue. Any number of patterns with a ground in the aforementioned colors would be great as well. Since midnight blue splits the difference between blue and black, two colors to avoid are navy blue or black. Same goes for yellow or pink, but you probably didn’t need me to tell you that. Anything in a light, cool color and you’ll knock ‘em dead.