Perhaps people didn't need a word for blue because they could say "the color of sky". For example the English word "green" comes from "grow" in PIE, meaning "th

Perhaps people didn't need a word for blue because they could say "the color of sky". For example the English word "green" comes from "grow" in PIE, meaning "the color of (plant) growth". Even "yellow" comes from "grow" although the sound changes there are significant enough that it's not as obvious as "green" is.