Ideally, whenever we use color map (with a particular colorscale), we should show users the color bar which shows how the values are mapped into the marker color. Whenever marker.colorscale is changing, this colorbar should change too. We also need to make sure the colorbar is on the opposite side of yaxis.

As of June 2017, Plotly had a few issues with marker.colorbar display: two tick sets would show up and colorbar would not update when new marker.colorscale is used.