Re: Insulators on D&RG pole lines?

For the most part, purple insulators are the only ones that have changed color.

Glass is naturally an aqua color, due to iron in the silica sands used for production. The darkness of that aqua color is dependent upon the quality of sands used. Various additives or other scrap glass used in production will change the glass color. Cobalt produces rich blues, while other mineral additions create dark greens and amber glass.

Prior to WWI, manganese was primarily used to decolorize glass in the US. When left out in the sun, this clear glass reacts with UV radiation and turns purple. Later insulator production used different decolorizing agents that don't turn purple.

Insulators were mass-produced industrial items. Some were intentionally colored, while most weren't. As such, they were unintentionally produced in a literal rainbow of colors.