'Pale' is an archaic English word derived from French referring to a territory surrounding a city. The two most common historical uses were the Pale of Dublin and the Pale of Calais. In both cases there was a period when this was the only area the English crown controlled in an otherwise alien territory, so going 'beyond the pale' was considered risky or at least confusing, hence the expression. It has no relation to the adjective 'pale'.

The pale is a place in Ireland that was under English administration in the late middle ages. Pale also has a another meaning, a stake supporting a fence, such as the one that divided the English ruled pale from the rest of Ireland. So anything beyond the pale, in this context, means anything beyond the boundary of English ruled Ireland.