White Huns, Red Huns, Black Huns, & Blue Huns: Persia & India against the Steppe

In the middle of the fourth century, various groups of people that Indian sources collectively refer to as "Huna" or "Hyon". Among them are the Kidarites, the Alchons, and possibly the Hepthalites. The Hepthalites and Alchons are also known as the "White Huns" and the "Red Huns" in some sources. Some recent work in linguistics is leading towards an argument that, if these Huns are truly derived from the Xiongnu, then it is possible that the color designations refer to directions and levels of importance among the Central Asian nomads, which would also mean that there were possibly "Blue Huns" and "Black Huns" as well. Dealing with the subject is, however, fairly difficult because we generally lack written records from the area and are reliant upon limited archaeology.
SOURCES:
Huns & Xiongnu: New Thoughts on an Old Problem, Atwood
Huns et Xiongnu, de la Vaissiere
The Huns, Kim
The Alkhan: A Hunnic People in South Asia, Bakker
Masters of the Steppe, Pankova & Simpson