title: small scatter plot markers in matplotlib are always black
body: <p>I'm trying to use matplotlib to make a scatter plot with very small gray points.  Because of the point density, the points need to be small.  The problem is that the scatter() function's markers seem to have both a line and a fill.  When the markers are small, only the line is visible, not the fill, and the line isn't the right colour (it's always black).</p>
  
  <p>I can get exactly what I want using gnuplot: plot 'nodes' with points pt 0 lc rgb 'gray'</p>
  
  <p>How can I make very small gray points using matplotlib scatterplot()?</p>