Is colored thread incorporated into rope construdtion to indicate rope strength and if so what color for what strength?

No. Colored threads are used merely for identification of the type of rope made by a particular manufacturer. Most ropes are available in identical styles, but varying diameters. The varying sizes of the same style of rope will all have the same color pattern.

For example, Yale Cordage, a rope company in Maine makes a rope called

Double Esterlon. It is available in 18 different diameters ranging from 1/4" thick to 2" thick. All sizes have the same color pattern- white rope with 4 green strands lying next to each other.

For proof, you can see this rope at http://www.yalecordage.com/html/pdf/industrial_marine/low/Pg8.pdf