A $p$-centered coloring for the grid using $O(p)$ colors

A $p$-centered coloring of a graph $G$, where $p$ is a positive integer, is a coloring of the vertices of $G$ in such a way that every connected subgraph of $G$ either contains a vertex with a unique color or contains more than $p$ different colors. We give an explicit construction of a $p$-centered coloring using $O(p)$ colors for the planar grid.