Colour (or label) a 3x3 square grid with three colours so that every square (1x1) is neighboured at least once by both of the remaining colours which aren't contained within that square.
Hello, Obsidantion!
Colour (or label) a 3x3 square grid with three colours
so that every 1x1 square is neighboured at least once by both of the
remaining colours which aren't contained within that square.
If I understand the problem, this is a solution.
. . $\displaystyle \begin{array}{|c|c|c|}\hline
{\color{red}\blacksquare} & {\color{green}\blacksquare} & {\color{red}\blacksquare} \\ \hline {\color{blue}\blacksquare} & {\color{blue}\blacksquare} & {\color{blue}\blacksquare} \\ \hline {\color{green}\blacksquare} & {\color{red}\blacksquare} & {\color{green}\blacksquare} \\ \hline \end{array}$