Well-dressed men wear cotton and linen pocket squares with worsted suits and silk versions with odd jackets and tweed or flannel suits. The sheen of the silk is best against textured jackets. Both the pattern and the ground color of the square should differ from the day's necktie.
A cream printed silk with blue and yellow flowers coordinates ever so discreetly with a light blue shirt.
A combination of colored squares on a steel blue ground complements a navy necktie.
And large gold paisleys are comfortable on a navy ground against gray flannel as well as brown tweed jackets.
Each square has hand-rolled edges and is 16 1/2" (42 cm) on a side so it remains visible in a pocket. $90 for one, including shipping in the continental United States, from A Suitable Wardrobe.