title: Using Seaborn split violin plots and palettes
body: <p>I'm creating a set of grouped violin plots with the following:</p>
  
  <pre><code>fig = plt.figure(1)
  
  ax1 = fig.add_subplot(3,1,1)
  sns.violinplot(x='x', y='y1', data=df_y1_all, split=True, inner=None, hue="hues_param", palette={"left":"r","right":"b"})
  ax1.legend()
  
  ax2 = fig.add_subplot(3,1,2)
  sns.violinplot(x='x', y='y2', data=df_y2_all, split=True, inner=None, hue="hues_param", palette={"left":"r","right":"b"})
  
  ax3 = fig.add_subplot(3,1,3)
  sns.violinplot(x='x', y='y3', data=df_y3_all, split=True, inner=None, hue="hues_param", palette={"left":"r","right":"b"})
  ax3.legend('')
  
  plt.show()
  </code></pre>
  
  <p>Which creates something like the following (I've omitted some of the sensitive parameter names as this is pre-published work):</p>
  
  <p><a href="https://i.stack.imgur.com/laDPT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/laDPT.png" alt="plot"></a></p>
  
  <p>I'd like to have a gradient of reds and a gradient of blues as per the argument <code>palette={"left":"r","right":"b"}</code>, but when I try to pass names of color palettes I get an error:</p>
  
  <p><code>ValueError: Could not generate a palette for ['Blues', 'Reds']</code> or for any other 'named' Seaborn palette.</p>
  
  <p>As my data is sensitive I can't share the original dataframe, but it's based on the working example from the <a href="http://seaborn.pydata.org/examples/grouped_violinplots.html" rel="nofollow noreferrer">docs</a>:</p>
  
  <pre><code>import seaborn as sns
  sns.set(style="whitegrid", palette="pastel", color_codes=True)
  
  # Load the example tips dataset
  tips = sns.load_dataset("tips")
  
  # Draw a nested violinplot and split the violins for easier comparison
  sns.violinplot(x="day", y="total_bill", hue="sex", data=tips, split=True,
                 inner="quart", palette={"Male": "b", "Female": "y"})
  sns.despine(left=True)
  </code></pre>
  
  <p>Which produces:</p>
  
  <p><a href="https://i.stack.imgur.com/JgY9M.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JgY9M.png" alt="plot2"></a></p>
  
  <p>Is there anyway to control the palette gradient or call a pre-made gradient within the plot arguments?</p>
  
  <p>Thanks!</p>