\documentclass[varwidth=true, border=2pt]{standalone}
\usepackage{ifthen}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\tikzstyle{vertex}=[draw,black,fill=blue,circle,minimum size=10pt,inner sep=0pt]
\tikzstyle{edge}=[very thick]
\begin{tikzpicture}
    \node (a)[vertex,fill=lime] at (1,0) {};
    \node (b)[vertex,fill=red]  at (0,1) {};
    \node (c)[vertex,fill=lime] at (1,2) {};
    \node (d)[vertex,fill=blue] at (2,2) {};
    \node (e)[vertex,fill=red]  at (3,1) {};
    \node (f)[vertex,fill=blue] at (2,0) {};

    \draw[edge] (a) -- (b) -- (c) -- (d) -- (e) -- (f) -- (a) -- cycle;
    \draw[edge] (b) -- (f);
    \draw[edge] (b) -- (d);
\end{tikzpicture}
\end{document}