title: Plotly colorscale reverse direction
body: <p>How can I reverse the direction of a colorscale in plotly? I am trying to use the <a href="https://plot.ly/python/line-and-scatter/#scatter-with-a-color-dimension" rel="noreferrer">color scale Viridis for a marker plot</a></p>
  
  <pre><code>import plotly.graph_objs as go
  import plotly.plotly as py
  
  import numpy as np
  
  trace1 = go.Scatter(
      y = np.random.randn(500),
      mode='markers',
      marker=dict(
          size=16,
          color = np.random.randn(500), #set color equal to a variable
          colorscale='Viridis',
          showscale=True
      )
  )
  data = [trace1]
  
  py.iplot(data, filename='scatter-plot-with-colorscale')
  </code></pre>
  
  <p>but I want it to be darker for higher values and lighter for lower values. Is there any way to do this without defining my own custom colorscale or changing my color parameter array?</p>