When <tt>plot_color_axis = 0</tt>, the array <tt>color_ind[i]</tt> is the same as
<tt>EPOT_IND[i]</tt>.  This means that the potential energy contribution of each atom
is used to determine the color of atoms (when <tt>plot_color_windows</tt> is activated).

<p>
When <tt>plot_color_axis = 2</tt>, the array <tt>color_ind[i]</tt> is the same as
<tt>TOPOL[i]</tt>.  This means that the central symmetry parameter
is used to determine the color of atoms (when <tt>plot_color_windows</tt> is activated).

<p>
Also see <tt>plot_color_windows</tt>.

