title: Color based on year in bokeh
body: <p>So I've basically got this snippet of code:</p>
  
  <pre><code>import pandas as pd
  from bokeh.plotting import figure, ColumnDataSource
  from bokeh.io import show, output_file
  import bokeh.models as bmo
  
  data = {
          'ranking': df['ranking'],
          'pct_intl_student' : df['pct_intl_student'],
          'years': year_list,
          'color': colors,
          'university':df['university_name']
  }
  
  source = ColumnDataSource(data)
  hover = bmo.HoverTool(
              tooltips=[('year', '@years'),
                        ('ranking', '@ranking'),
                        ('% Int. Stu.', '@pct_intl_student'),
                        ('University', '@university')])
  
  
  
  p = figure(tools=[hover], title="Scatterplot: International Students")
  p.xaxis.axis_label = 'International Ranking'
  p.yaxis.axis_label = 'Pct. International Students'
  
  p.scatter('ranking', 'pct_intl_student', source=source)
  
  show(p)
  </code></pre>
  
  <p>Where color is basically a list that has a color that corresponds to every datapoint in ranking and pct_intl_student. Basically, they're the same length. Would it be possible to make sure that every datapoint that I plot in the scatterplot has the color as specified in the colors list? I figured it would just be some attribute of the figure, but can't find it easiliy in the documentation. All data is retrieved from a dataframe and I created the color mapping as such:</p>
  
  <pre><code>colormap = {2016: 'red',
              2017: 'green',
              2018: 'blue'}
  colors = [colormap[x] for x in df['year']]
  </code></pre>