@madnigeWhatever.
The point is, the distinction between the two Russian words for blue shades has nothing at all to do with indigo, with is far to the red from the pure blue синий with corresponds well with my understanding of English "blue", and the RGB blue peak. While the other word, the "pigeonish" color is either less saturated or way to the green, most easily referred to by cyan instead as far technical color names go.
Russian "blue sky" is голубое небо while the school uniform is dark intense blue синий. Neither of two has any notable red component in it. Indigo, or any approximations thereof, definitely do have, and everything even a little to the red of pure blue is "purple" for all people I know (in real life).
Russian isn't my native language, but have had to study it from age 7, against my will, and tolerate environments with significant percentage of native Russian speakers ever since. I still avoid writing it if I can, it's a pain, but I read freely, understand well, and can speak if needing. So, yes, I can't talk to the meanings of those words with the certainty of a native, but have had to develop fairly good concept about the possibilities of the meaning space of each.
To repeat, it's as much to do with, indeed, intensity and saturation of the color than, or rather not only, wavelength. The голубой is pale-blue, like the sky by the horizon, while
My native language (latvian) doesn't have a word for голубой/cyan either, it's all blue zils, until it's bluish-green zilganzaļš but that's already beyond cyan into the green. While even slightly reddish-blue is already