This is related to a [previous question][1] that I asked.

The *degeneracy* of a graph $G$, denoted $\mathrm{degen}(G)$, is given by $\max\{\delta(H): H\subseteq G\}$.  It is well known that for all graphs $G$, $\chi(G)\leq \mathrm{degen}(G)+1\leq \Delta(G)+1$.  [Brooks' theorem][2] characterizes graphs with $\chi(G)=\Delta(G)+1$.  

Is there a characterization of graphs $G$ with $\chi(G)=\mathrm{degen}(G)+1$?

The example given by Mikhail Tikhomirov in response to my previous question (where $\chi(G)=4$ and $\mathrm{degen}(G)=3$) suggests that if there is a characterization, it will be much more complicated than the one given by Brooks' theorem.  So any properties which imply $\chi(G)=\mathrm{degen}(G)+1$ would be interesting.

Note that the degeneracy plus 1 is also referred to as the *coloring number*, and is denoted $\mathrm{col}(G)$. So my question can also be phrased as "Is there a characterization of graphs $G$ with $\chi(G)=\mathrm{col}(G)$?"


  [1]: https://mathoverflow.net/questions/375292/replacing-maximum-degree-with-degeneracy-in-reeds-conjecture
  [2]: https://en.wikipedia.org/wiki/Brooks%27_theorem