Reference Request: Asymptotic hardness of $hk$ coloring $k$-colorable graphs
Here are the references:


S. Khanna, N. Linial, and S. Safra, On the hardness of approximating the chromatic number,
Combinatoria, 20 (2000), pp. 393–415.
C. Lund and M. Yannakakis, On the hardness of approximating minimization problems, J.
ACM, 41 (1994), pp. 960–981.