title: wxColourProperty set/get value as wxColour
body: <p>Using wxColourProperty, I cannot work out how to get the value as a wxColour or set the value as a wxColour reliably?</p>
  <p>Within advprops.cpp, I can see plenty of code for setting it (including the inline template specialization WXVARIANT), but if I try to do the same myself the colour RGB values are set and visible in the property grid but the actual colour is still wxWHITE in the preview blob in the property grid element.</p>
  <p>eg.</p>
  <pre><code>// Assuming property is wxPGProperty*
  wxColour myColour = *wxBLUE;
  wxColourPropertyValue cpv;
  cpv.Init(wxPG_COLOUR_CUSTOM, c.IsOk() ? c : *wxWHITE);
  wxVariant variant;
  variant &lt;&lt; cpv;
  property-&gt;SetValue(variant);
  </code></pre>
  <p>This doesn't work. I am trying to set the value of the property after initial construction.</p>
  <p>I can't even work out how to get a wxColour from a wxColourProperty - any ideas?</p>
  <p>I am using wxWidgets 3.1.something that I built from a git fetch a couple of months before 3.2 was released. I am using Ubuntu 20.04 LTS.</p>