A counterchange (not a countercharge) in heraldry/vexillology is when two colors alternate in different parts of the coat of arms or flag. Two examples I know of in flags:
The UK Union Jack is composed of three crosses. One is the red verticle/horizontal St George’s Cross; the other two are saltires (Xs from corner to corner). One is red and the other white. If you look carefully, you’ll notice that on the hoist side, the white is on top while on the fly, the red is on top. This alteration is a counterchange.
Here’s what it looks like without St George’s Cross:
A more obvious counterchange is the Greenland flag, which is a white and red horizontal bicolor with a counterchanged circle.
Are there any other examples of counterchange in national/subnational flags?
How come? I’d say that the Taeguk/Yin-Yang symbol is a classic example of a countercharge - “two colors alternate in different parts of the coat of arms or flag”.