Most city ensembles should be kept to no more than two patterns above the waist, in my opinion (that encompasses shirt, necktie, pocket square and jacket). Adding a third pattern is often too eye-catching, and can be difficult to do successfully in the first place. The patterns must be of different scales, should be of different types (no dotted squares with dotted neckties for example), and the colors complementary but not matching.
Outside of the center of a large city, life is generally less formal and the third (indeed, occasionally even a fourth) pattern finds easier acceptance. In the photo, the same striped silk jacquard necktie and medallion print wool and silk pocket square that were worn with a gray odd jacket in an earlier post are paired with a brown glen check suit and a light blue twill shirt for a day in the suburbs.