\documentclass[preview=false,box=true,tikz,border=0pt]{standalone}
\begin{document}
\begin{tikzpicture}
\draw (0,0) rectangle (5,6);
\draw (0,0) -- (5,6);
\end{tikzpicture}
\begin{tikzpicture}
\shade [left color=blue, right color=green] (0,0) rectangle (5,10);
\end{tikzpicture}
\begin{tikzpicture}[green]
\draw (0,0) rectangle (6,8);
\draw (0,0) -- (6,8);
\end{tikzpicture}
\begin{tikzpicture}[red]
\draw (0,0) rectangle (2,3);
\draw (0,0) -- (2,3);
\end{tikzpicture}