  Given a graph $G$, a vertex-colouring $\sigma$ of $G$, and a subset
$X\subseteq V(G)$, a colour $x \in \sigma(X)$ is said to be \emph{odd} for $X$
in $\sigma$ if it has an odd number of occurrences in $X$. We say that $\sigma$
is an \emph{odd colouring} of $G$ if it is proper and every (open)
neighbourhood has an odd colour in $\sigma$. The odd chromatic number of a
graph $G$, denoted by $\chi_o(G)$, is the minimum $k\in\mathbb{N}$ such that an
odd colouring $\sigma \colon V(G)\to [k]$ exists. In a recent paper, Caro,
Petru\v sevski and \v Skrekovski conjectured that every connected graph of
maximum degree $\Delta\ge 3$ has odd-chromatic number at most $\Delta+1$. We
prove that this conjecture holds asymptotically: for every connected graph $G$
with maximum degree $\Delta$, $\chi_o(G)\le\Delta+O(\ln\Delta)$ as $\Delta \to
\infty$. We also prove that $\chi_o(G)\le\lfloor3\Delta/2\rfloor+2$ for every
$\Delta$. If moreover the minimum degree $\delta$ of $G$ is sufficiently large,
we have $\chi_o(G) \le \chi(G) + O(\Delta \ln \Delta/\delta)$ and $\chi_o(G) =
O(\chi(G)\ln \Delta)$. Finally, given an integer $h\ge 1$, we study the
generalisation of these results to $h$-odd colourings, where every vertex $v$
must have at least $\min \{\deg(v),h\}$ odd colours in its neighbourhood. Many
of our results are tight up to some multiplicative constant.
