Qara Turk/Kara Turk/"Black Turk"

I grew up in a village in Kashgar. When I was a kid, I heard the word "Qara Turk" used frequently among the people in my town. It was interesting that some people still would not identify themselves as Uyghurs or could not pronounce Uyghur correctly (they used Urghuy). But somehow, they always called themselves "Qara Turk", as indicative of their illiteracy, or to say they were poor or had low social status. As such, "Qara Turk" also became a word for insulting someone as uneducated, illiterate, or brute.

In later years, I learned history, especially the history of Kok Turks (GokTurks), and I realized where the Qara Turk came from. My theory is that GokTurks identified themselves as a noble, ruling class, and all the other Turks were called Qara Turks, as low class, like calling "you peasants":D. I don't think the word "Qara" here indicates geographical direction as in other cases.

I am interested if other Turkic people have the word "Qara Turks" with similar meanings.