What were the Eunuchs exactly!?

[Renatus]

. . . that's the origin of the saying "cum pedibus albis", it most likely denotes foreign origin . . .

I wonder if this is in any way analogous to the name of the ancient English system of Courts of Piepowder, which administered justice at fairs and markets. The name is usually explained as referring to the 'dusty feet' (pieds poudrés in French) of those who had travelled to the location. A similar explanation might relate to the ‘white (or dusty) feet’ of those who had travelled from outside the Empire.