Minimum chromaticity of circulant graphs

We determine families of circulant graphs for which each graph G=Gc(n;S) has chromatic number χ(G)⩽3. In particular, we show that there exists an n0 such that χ(G)⩽3 for all n⩾n0 whenever S={s1,s2,…,sk} and sk>sk-1>⋯>s1 and 2s1>sk or S={s1,s2} and s2>s1⩾1 and s2≠2s1. We also prove that χ(G)⩽3 for every recursive circulant graph G=RGc(n;d), n=cdm, 1