title: Altair selection with different colours
body: <p>I started playing around with Altair today and have a question about selections. I have created 3 bar charts with different colours as shown below. Now whenever I click on one bar, I'd like the equivalent to be highlighted in the other two bar charts. This works well if I don't use any colour and it defaults to blue, but I can't figure out how to keep my colours in the selection instead of having the same colour for all 3 charts.</p>
  
  <p><a href="https://i.stack.imgur.com/NFNRR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NFNRR.png" alt="enter image description here"></a></p>
  
  <pre><code>df = pd.DataFrame({"Name":["Bulbasaur", "Charizard", "Mewtwo"], 
                    "HP":[45, 80, 100], 
                    "Attack":[30, 50, 60], 
                    "Defense":[40, 38, 42], 
                    "Type":["Grass", "Fire", "Psychic"]}) 
  
  
  selection = alt.selection_single(fields=["Type 1"])
  
  # This doesn't do much as I don't have a column named #73a1eb. But it's the colour code I'd like to use.
  color1 = alt.condition(selection,
                    alt.Color("#73a1eb:N", legend=None), 
                    alt.value('lightgray'))
  
  color2 = alt.condition(selection,
                    alt.Color("#73b9c7:N", legend=None),
                    alt.value('lightgray'))
  
  color3 = alt.condition(selection,
                    alt.Color("#d7abf5:N", legend=None),
                    alt.value('lightgray'))
  
  # The mark bar colour is overriden by color in encode
  
  chart1 = alt.Chart(df, title="Average HP by Type")
              .mark_bar(color="#73a1eb", size = 12)
              .encode(x = 'mean(HP):Q',
                      y = alt.Y('Type 1:N', sort='-x'), 
                      tooltip=["Type 1", "mean(HP):Q"], 
                      color=color1)
              .properties(height=320,
                          width=300)
              .add_selection(selection)
  
  chart2 = alt.Chart(df, title="Average Attack by Type")
              .mark_bar(color="#73a1eb", size = 12)
              .encode(x = 'mean(Attack):Q',
                      y = alt.Y('Type 1:N', sort='-x'), 
                      tooltip=["Type 1", "mean(HP):Q"], 
                      color=color1)
              .properties(height=320,
                          width=300)
              .add_selection(selection)
  
  chart2 = alt.Chart(df, title="Average Defense by Type")
              .mark_bar(color="#73a1eb", size = 12)
              .encode(x = 'mean(Defense):Q',
                      y = alt.Y('Type 1:N', sort='-x'), 
                      tooltip=["Type 1", "mean(HP):Q"], 
                      color=color1)
              .properties(height=320,
                          width=300)
              .add_selection(selection)
  
  alt.hconcat(chart1, chart2, chart3).configure_axis(grid=False).configure_axisBottom().resolve_scale(x = 'shared')
  </code></pre>