Number of vertices in graphs with locally small chromatic number and   large chromatic number
  We discuss the minimal number of vertices in a graph with a large chromatic number such that each ball of a fixed radius in it has a small chromatic number. It is shown that for every graph $G$ on $\sim((n+rc)/(c+rc))^{r+1}$ vertices such that each ball of radius $r$ is properly $c$-colorable, we have $\chi(G)\leq n$. 
Ilya I. Bogdanov
math.CO