A very specific case of Reed's Conjecture
Reed's $\omega$,$\Delta$, $\chi$ conjecture proposes that every graph has $\chi \leq \lceil \tfrac 12(\Delta+1+\omega)\rceil$. Here $\chi$ is the chromatic number, $\Delta$ is the maximum degree, and $\omega$ is the clique number.
When restricted to triangle-free graphs, the equivalent question is, Does every triangle-free graph have chromatic number $\leq \frac \Delta 2 +2$?
This is known for $\Delta\leq 4$. In general for triangle-free graphs, $\chi \leq O(\Delta/\log \Delta)$, so the conjecture is also true for very large $\Delta$.
How about $\Delta=5$? $\Delta=6$? Because of parity, $\Delta=6$ is the easier of these two cases (and actually easily implies the $\Delta=5$ case. Can anyone prove it?
Kostochka proved that every triangle-free graph has $\chi \leq \frac 2 3 \Delta +2$. He also proved that $\chi\leq \frac \Delta 2 +2$ for graphs of sufficiently large girth depending on $\Delta$. Can anyone prove it for girth $\geq 5$? $4$?
This would at least provide some hope for proving Reed's Conjecture for triangle-free graphs.
Does every triangle-free graph with $\Delta\leq 6$ have $\chi \leq 5$? What about every graph with girth at least five?