If its truly a "suit" then the coat and slacks should match.
That said, every so often (approx 30 years or so), we see the re-emergence of the dissimilar coat and slacks set. When I was working at Baskins (a now defunct clothing store chain in the Chicago area; specialized in the very conservative Hart, Shaffner and Marx brand) some <mumble 30+> years ago, they occasionally had suits with 2 sets of slacks. The non-matching slacks were always plain (i.e. non-patterned). Nowadays, we have the euphemistically monikered "suit separates" (which, when I first heard the term, thought was referring to ladies clothing). This gambit appears to be the same thing as the Baskin 2-slacks thing, except without the 2nd pair of slacks.
Basically, my OF (old fogey) counsel would be this: If you're in a business attire situation where "dressing for success" (and all that implies) is required, do one of the following:
* Wear a suit, wit the slacks matching the suit coat.
* Wear a sportcoat and coordinating slacks.
* Never wear patterned slacks with anything other than a matching coat.