Hatching is a way of showing heraldic colours using only monochrom images. All of the common heraldic colours have a corresponding Hatching, as do some of the more modern colours. If a colour does NOT have a hatching then a plain grey is shown.
Hatching works best on simple shields; for two main reasons, complex shields just become a blur of indistinguishable lines; and sometimes charges which are rotated and inverted can also cause the hatching to rotate with them, rendering them incorrect. In particular, this will happen to a charge that is place on another charge that is itself rotated.