title: Python matplotlib manual colormap
body: <p>I have 2-d fields to plot in python using matplotlib basemap. 
  The values of the fields varies from 0 to more than 1000. Is it possible to create manual colormap with fixed gradations and colours? It should looks like :</p>
  
  <p>for values    - set colour     </p>
  
  <ul>
  <li>0 - 1      -     white</li>
  <li>1 - 5      -     dark green </li>
  <li>5 - 10     -     light green</li>
  <li>10 - 25    -     yellow</li>
  <li>25 - 50    -     brown</li>
  <li>50 - 100   -     orange</li>
  <li>100 - 500  -     light red</li>
  <li>500 - 1000 -     dark red</li>
  <li>> 1000     -     purple</li>
  </ul>
  
  <p>I am a new in python. So, any suggestions are welcome.</p>