There are no black-and-whites rule for this
One rule of the thumb is that white pocket squares go with anything. Other than that, you can color-coordinate a pocket square with your shirt or trousers, but never match it with the exact color or pattern of your tie, which makes it look like you went for a buy-one-get-one deal for those two accessories.
Sometimes, it’s also great to have a very colorful pocket square to balance out a plain black suit—at least it’ll help set you apart from the rest of the penguin-looking guests at a party.
Better yet, pick the ones that suit your personality and wear them with confidence.