\documentclass[]{standalone}
\usepackage{tikz}

\begin{document}
   \begin{tikzpicture}
       \node [circle, fill=blue, opacity=0.5, minimum size=.4cm] 
           at (0.2cm,0cm) () {};
       \node [circle, fill=red, opacity=0.5, minimum size=.4cm]
          at (0cm,0cm)  () {};
       \node [circle, fill=green, opacity=0.5, minimum size=.4cm] 
          at (0.1cm,0.2cm)  () {};
          
       \node at (0,0) {$T=\T$};
   \end{tikzpicture}
\end{document}