File:Hemitetrahedron.svg

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \newcommand\rsize{1.5}
  \path(2,2)--(-2,-2);
  \fill[gray](\rsize,\rsize)--(-\rsize,\rsize)--(-\rsize,-\rsize);
  \fill[gray!70!white](\rsize,\rsize)--(\rsize,-\rsize)--(-\rsize,-\rsize);
  \begin{scope}[very thick,inner sep=0.7mm,minimum width=5mm,circle]
    \node[draw=black, thick, fill=red ](V0)at( \rsize, \rsize){\large a};
    \node[draw=black, thick, fill=cyan](V1)at(-\rsize, \rsize){\large b};
    \node[draw=black, thick, fill=red ](V2)at(-\rsize,-\rsize){\large a};
    \node[draw=black, thick, fill=cyan](V3)at( \rsize,-\rsize){\large b};
  \end{scope}
  \draw[very thick,inner sep=0.3mm, circle]
    (V0)
    --node[draw=black, thin, fill=yellow]{\small1}(V1)
    --node[draw=black, thin, fill=purple]{\small2}(V2)
    --node[draw=black, thin, fill=yellow]{\small1}(V3)
    --node[draw=black, thin, fill=purple]{\small2}(V0)
    --node[draw=black, thin, fill=orange]{\small0}(V2);
  \node at(135:\rsize*.65){\Huge\textbf{I}};
  \node at(-45:\rsize*.65){\Huge\textbf{II}};
\end{tikzpicture}
\end{document}