A tight bound for conflict-free coloring in terms of distance to cluster

Given an undirected graph $G=(V,E)$, a conflict-free coloring with respect to open neighborhoods (CFON coloring) is a vertex coloring such that every vertex has a uniquely colored vertex in its open neighborhood. The minimum number of colors required for such a coloring is the CFON chromatic number of G, denoted by ${\chi }_{ON}(G)$.In previous work [WG 2020], we showed the upper bound ${\chi }_{ON}(G)\le \mathsf{dc}(G)+3$, where $\mathsf{dc}(G)$ denotes the distance to cluster parameter of G. In this paper, we obtain the improved upper bound of ${\chi }_{ON}(G)\le \mathsf{dc}(G)+1$. We also exhibit a family of graphs for which ${\chi }_{ON}(G)>\mathsf{dc}(G)$, thereby demonstrating that our upper bound is tight.