A pocket square should be chosen to coordinate with, not match, the tie. An identically matching tie and pocket square do contribute to an interesting appearance. In addition, blocks of the same color pull eyes away from the wearer's face to the chest.
Pocket squares and ties should coordinate by pattern or color. If the tie is striped, the pocket square picks up a bit of the tie color but uses a different stripe or even a plaid. If the emphasis is on color, one option is a solid pocket square that takes its color from the tie. Alternately, a dotted or paisley pocket square uses the same colors as the tie.