title: Conditional color with matplotlib scatter
body: <p>I have the following Pandas Dataframe, where column a represents a dummy variable:</p>
  
  <p><img src="https://i.stack.imgur.com/FBLXN.png" alt="Panda Dataframe"></p>
  
  <p>What I would like to do is to give my markers a <code>cmap='jet'</code> color following the value of column <code>b</code>, except when the value in column <code>a</code> is equal to 1 - in this case I want it to be the color grey.</p>
  
  <p>Any idea how I can do this?</p>