...can you tell which one of these insulators is not like the others? Think Sesame Street...

Left to right:

CD 130.1 Cal. Elec. Works in cobalt blue

CD 262 Columbia #2 L.S.V. in light cornflower blue

CD 123 EC&M in steamy, fizzy dark aqua

CD 128 Hemingray E-14B in medium opalescent