\begin{tikzpicture}[rotate=-90, scale=0.2]
\def\n{50}
\pgfmathparse{\n+1}
\xdef\nn{\pgfmathresult}
\foreach \i in {1,...,\n} {
	\foreach \j in {1,...,\n} {
		\pgfmathparse{\i+2}
		\ifthenelse{\j=\pgfmathresult}{
			\draw[fill=red] (\i-1,\j-1)--(\i,\j-1)--(\i,\j)--(\i-1,\j)--(\i-1,\j-1);
		}{
			\ifthenelse{\j=\i}{
			\draw[fill=blue] (\i-1,\j-1)--(\i,\j-1)--(\i,\j)--(\i-1,\j)--(\i-1,\j-1);
		}{
			\draw (\i-1,\j-1)--(\i,\j-1)--(\i,\j)--(\i-1,\j)--(\i-1,\j-1);
		}	
		}
	}
}
\end{tikzpicture}