The following are some of the transcriptions of Qarluq
Türük: 𐰴𐰺𐰞𐰸
Türki: قَرْلُق
Chinese: 葛邏祿
Persian: خَلُّخ
Arabic: قارلوق
Typically, Türük 𐰴𐰺𐰀 transcribes qɑrɑː "black; dark; common (people);" however, this is likely due to the word's final long vowel. For example, Türük 𐰴𐰺𐰍𐰆 transcribes qɑrɑğuː "watchman, sentry." Thus, the word transcribed by 𐰴𐰺 seems to be qɑrɑ; a conclusion supported by the trisyllabic Chinese transcription 葛邏祿. What, then, to make of 𐰞𐰸. Since Türki, Persian, nor Arabic differentiates between o and u, there is no guarantee that we are looking at -luq. In any case, this would violate vowel harmony; since, the correct suffix for qɑrɑ would be -lıq. In theory, 𐰞𐰸 could transcribe -lıq, but the non-Türük transcriptions make it clear that we are dealing with an o or u. So, we are ultimately dealing with one of the two:
Qɑrɑloq
Qɑrɑluq
However, the simplest explanation is that the confederacy's name was indeed Qaralıq initially, but that over time, ı became u. This sort of sound change would not be irregular.