Odd colors are desirable.
A multitude of grays, greens, blues, yellows, and cobalt's can be found. Like glass pieces with snow or swirling, many porcelain insulators have very unusual mottling , drips, or color mixing on an otherwise common colored piece. These all command a premium. Imperial, General Electric, Peru, Fred Locke, and R. Thomas and Sons all produced mostly white insulators until the turn of the century, when brown glaze came into favor to deter vandals. Many white insulators actually have clear glaze, and the white ceramic of the insulators shows through.