title: colors in matplotlib with respect of intensity
body: <p>I'm wondering how to plot colors with respect of intensity using python.
  For example I have a list [0.1, 0.5, 1.0], and I would like to plot circles with darkest circle on 1.0, and second darkest circle for 0.5 and third darkest circle for 0.1.</p>
  
  <p>Thanks a lot for helping.</p>