I can't help wondering why they bothered to make them in colors given that this is basically a ultitarian item. Could the colors be some kind of code in themselves ??
Hi... it is
nice they come in colors, isn't it? To insulator collectors, "color" means anything but
aqua shades or clear. As the alert reader knows, a glass batch is usually some shade of aqua due to trace iron in the sand; greens
were often the results of amber cullet mixed into the batch; purples
are due to the manganese decolorizer solarizing, same for straw
(selenium); carnival glass(tin oxide) is a radio treatment; milkglass was made to simulate white porcelain (for neutral lines), blackglass to simulate the usual brown/black glaze of porcelain (these last two in a desperate attempt to compete with porcelain manufacturers once glass use was in decline).
As for the other colors, most insulators were a sideline of glasshouses, so they tended to use up batches by cranking some insulators out, so you get the nice colors they intended for tableware, oil lamps, etc.
Some colors were made on purpose: you could
(cobalt, peacock, etc) insulators from Hemingray for use in marking specific lines on crowded crossarms; in this case, the color was
a code, but it was up to the end user to define, there's no standard. The same batches were used in making their other products, so you can find insulators and oil lamps in identical shades, insulators and matching frigerator bottles, etc.
As for the amber shades of Dominions, probably that glass was used for other purposes, likely [beer? medicine?] bottles-- glasshouses only made so many batches, perhaps just one or two at a time (say, clear and a color); if they made up a big amber tank, or had a continuous amber tank, they would crank out all sorts of products with the same color, insulators included.
All in all, they were all sorts of colors because noone cared! It didn't matter for the functionality, so any color was fine. Later on, they started specifying clear (better spider-nesting-resistance, less solar heat gain), and production got high quality and boring.
Pretty stuff in a windowsill!