title: matplotlib scatter plot colour as function of third variable
body: <p>I would like to know how to make matplotlib's scatter function colour points by a third variable.</p>
  
  <p>Questions
  <a href="https://stackoverflow.com/questions/8945699/gnuplot-linecolor-variable-in-matplotlib">gnuplot linecolor variable in matplotlib?</a> and <a href="https://stackoverflow.com/questions/8202605/matplotlib-scatterplot-colour-as-a-function-of-a-third-variable">Matplotlib scatterplot; colour as a function of a third variable</a>
  posed similar queries, however, the answers to those questions don't address my issue: the use of <code>c=arraywhichspecifiespointcolour</code> in the scatter function only sets the fill colour, not the edge colour. This means that the use of <code>c=arr...</code> fails when using <code>markersymbol='+'</code>, for instance (because that marker has no fill, only edges). I want points to be coloured by a third variable reliably, regardless of which symbol is used.</p>
  
  <p>Is there a way to achieve this with Matplotlib's scatter function?</p>