Radar plots, on the radarplot element properties area, have an option "vary
color by slice". This option also exists in pie plots where it behaves correctly
and makes sense. This option SHOULD NOT EXIST for radar plots. The "slices" are
actually different series which means that they colours can be controlled in the
series element properties. 

If this property is kept, please note that the box should start checked, since
by default we do vary the colours of the different series. Currently, checking
the box makes all the series share the colour of the first series.

--adrian