title: python scatter plot with errorbars and colors mapping a physical quantity
body: <p>I'm trying to do a quite simple scatter plot with error bars and semilogy scale. What is a little bit different from tutorials I have found is that the color of the scatterplot should trace a different quantity. On one hand, I was able to do a scatterplot with the errorbars with my data,  but just with one color. On the  other hand, I realized a scatterplot with the right colors, but without the errorbars.
  I'm not able to combine the two different things.</p>
  
  <p>Here an example using fake data:</p>
  
  <pre><code>#!/usr/bin/env python
  # -*- coding: utf-8 -*-
  from __future__ import division
  import numpy as np
  import matplotlib.pyplot as plt
  
  n=100
  Lx_gas = 1e40*np.random.random(n) + 1e37
  Tx_gas = np.random.random(n) + 0.5
  Lx_plus_error = Lx_gas
  Tx_plus_error = Tx_gas/2.
  Tx_minus_error = Tx_gas/4.
  
  #actually positive numbers, this is the quantity that should be traced by the
  #color, in this example I use random numbers
  Lambda = np.random.random(n) 
  
  #this is actually different from zero, but I want to be sure that this simple
  #code works with the log axis
  Lx_minus_error = np.zeros_like(Lx_gas)
  
  #normalize the color, to be between 0 and 1
  colors = np.asarray(Lambda)
  colors -= colors.min()
  colors *=  (1./colors.max())
  
  #build the error arrays
  Lx_error = [Lx_minus_error, Lx_plus_error]
  Tx_error = [Tx_minus_error, Tx_plus_error]
  
  ##--------------
  ##important part of the script
  
  ##this works, but all the dots are of the same color
  #plt.errorbar(Tx_gas, Lx_gas, xerr = Tx_error,yerr = Lx_error,fmt='o')
  
  ##this is what is should be in terms of colors, but it is without the error bars
  #plt.scatter(Tx_gas, Lx_gas, marker='s', c=colors)
  
  
  ##what I tried (and failed)
  plt.errorbar(Tx_gas, Lx_gas, xerr = Tx_error,yerr = Lx_error,\
          color=colors,  fmt='o')
  
  
  ax = plt.gca()
  ax.set_yscale('log')
  plt.show()
  </code></pre>
  
  <p>I even tried to plot the scatterplot after the errorbar, but for some reason everything plotted on the same window is put in background with respect to the errorplot.
  Any ideas?</p>
  
  <p>Thanks!</p>