here i found this hope it helps ... Color makes a big difference in value in general. For glass insulators clear and aqua (Blue-green glass) are by far the most common colors. Shades of green glass are next, more vivid green colors (depresion glass green probably the best) have more value. Next would be amber glass -- There are some Whitall Tatum and Armstrong insulators in a very dark amber, which are pretty common, but most other amber pieces are pretty good. White milk glass is common in only one style, the CD 164 Maydwell-20 which is still a $20.00 insulator. Purple glass is probably next with the CD 102 Diamond in royal purple and the purple CD 154 Whitall Tatum No. 1 being the most common (Still in the $20-$25 range). California embossed insulators also frequently come in purple glass. The best insulator color is cobalt blue (Or it's brighter cousin peacpck blue) -- these are very obvious vivid colors and all are in the $300+ value range if in good condition. Black-glass and opalescent are also sometimes found and are pretty good.
As for porcelain, colors are still very important for value and porcelain insulators tend to be more affordable than glass. Brown is by far the most common, followed by white or clear glaze (The porcelain is white so clear glazed pieces appear white). Next would be blue glaze -- cobalt blue (Very dark is more common than lighter shades). Blue porcelains tend to be in the $8-$20 range. Next would be green glazes ($10-$25 range), and then gray glazes ($8-$25). Next, Yellow glazes - the brighter the better ($8 for butterscotch colors, $10-$15 for pastel yellows, and $15-$30 for canary bright yellow). True black glazes are only known on a few styles (Make sure it is not just a dark brown or cobalt blue) - these go in the $30+ range. There are no known american porcelain insulators with red glazes, but there are british styles in fire engine red - These go in the $75+ range.
