"Beyond the pale" explained

Pale has nothing to do with the adjective for something light in colour except that both come from Latin roots. The one referring to colour originates in the Latin verb pallere, to be pale, whilst our one is from palus, a stake (also the name of the wooden post that Roman soldiers used to represent an opponent during fighting practice). Pale is an old name for a pointed piece of wood driven into the ground and — by an obvious extension — to a barrier made of such stakes, a palisade or fence. Pole is from the same source, as are impale, paling and palisade. This meaning has been around in English since the fourteenth century and by the end of that century pale had taken on various figurative senses — a defence, a safeguard, a barrier, an enclosure, or a limit beyond which it was not permissible to go...

In particular, the term was used to describe various defended enclosures of territory inside other countries. For example, the English pale in France in the fourteenth century was the territory of Calais, the last English possession in that country. The best-known example is the Russian Pale, between 1791 and the Revolution of 1917, which were specified provinces and districts within which Russian Jews were required to live...

The earliest figurative sense that’s linked to the idiom was of a sphere of activity or interest, a branch of study or a body of knowledge, which comes from the same idea of an enclosed or contained area; we use field in much the same way... Our sense seems part to have grown out of this, since people who exist outside such a conceptual pale are not our kind and do not share our values, beliefs or customs.

From World Wide Words.