While you can certainly do it, the fact remains that you still won't be wearing a suit. Wearing a navy blazer with navy pants for example won't look nearly as good, or dressy, as wearing that same blazer with some medium-dark gray pants; especially if that blazer has bright colored buttons.
A tailored jacket (aka sportcoat or blazer) paired with tailored trousers in a different fabric is not a suit. For instance, a navy blazer with gray tailored trousers: not a suit! This type of outfit is inherently less formal than a suit. A blazer paired with non-matching trousers is not a suit.
