title: Symmetric colormap matplotlib
body: <p>I have a series of values that varies between -180 to 180, I what a color map symmetric around zero, i.e. the color for -180 is the same for 180 values and so on. It is my first time using matplotlib I only don't find the way to make it symmetric around zero, the negatives always have different colors that the positives. 
  Thank you very much.</p>