Well, they're what you could call "formal". As per Vox's guide to coherent combinations: shirts are white, plain light blue or blue and white stripes; neckties are solid grenadines or other textured woven silks, wedding tie patterns in silk, silk prints with discreet non-repeating figurative patterns, or diagonally striped ties (unless you're British) without too much of a sheen; hanks are fine white linen. This doesn't mean you have to stick 100% to that stuff with a city suit, but it works best.
It all would work with a flannel suit if you don't rusticate it too much (i.e. patch pockets). If you decide to get flap pockets instead, then the suit could maybe work with both city and country accesories. Don't take it as a hard set of rules, but rather as a fairly safe way of doing things right.