Gladstone and Geiger apparently did not realize that glaucos in Greek, t'khelet in Hebrew, vinlla in Sanskrit, etc. refer to blue.
Generally the older the language the less clearly defined the vocabulary for colors is - but this applies to many categories: number, animals, and so on.
The ancients were able to see the sky as well as we can. They saw the same color we do. As each culture got better at creating blue dyes and paints, a technical vocabulary to describe color distinctions more distinctly developed.
Primitive tribes in South America and Polynesia will often use one word to describe all bright colors - but when asked to differentiate between the various primary and secondary colors through gestures they can do so as well as any Western housepainter.