old_contents: """
  Interactive Crossfilter
  =======================
  This example shows a multi-panel view of the same data, where you can interactively
  select a portion of the data in any of the panels to highlight that portion in any
  of the other panels.
  """
  # category: interactive charts
  import altair as alt
  from vega_datasets import data
  
  source = alt.UrlData(
      data.flights_2k.url,
      format={'parse': {'date': 'date'}}
  )
  
  brush = alt.selection(type='interval', encodings=['x'])
  
  # Define the base chart, with the common parts of the
  # background and highlights
  base = alt.Chart().mark_bar().encode(
      x=alt.X(alt.repeat('column'), type='quantitative', bin=alt.Bin(maxbins=20)),
      y='count()'
  ).properties(
      width=160,
      height=130
  )
  
  # blue background with selection
  background = base.add_selection(brush)
  
  # yellow highlights on the transformed data
  highlight = base.encode(
      color=alt.value('goldenrod')
  ).transform_filter(brush)
  
  # layer the two charts & repeat
  alt.layer(
      background,
      highlight,
      data=source
  ).transform_calculate(
      "time",
      "hours(datum.date)"
  ).repeat(column=["distance", "delay", "time"])
  
new_contents: """
  Interactive Crossfilter
  =======================
  This example shows a multi-panel view of the same data, where you can interactively
  select a portion of the data in any of the panels to highlight that portion in any
  of the other panels.
  """
  # category: interactive charts
  import altair as alt
  from vega_datasets import data
  
  source = alt.UrlData(
      data.flights_2k.url,
      format={'parse': {'date': 'date'}}
  )
  
  brush = alt.selection(type='interval', encodings=['x'])
  
  # Define the base chart, with the common parts of the
  # background and highlights
  base = alt.Chart().mark_bar().encode(
      x=alt.X(alt.repeat('column'), type='quantitative', bin=alt.Bin(maxbins=20)),
      y='count()'
  ).properties(
      width=160,
      height=130
  )
  
  # gray background with selection
  background = base.encode(
      color=alt.value('#ddd')
  ).add_selection(brush)
  
  # blue highlights on the transformed data
  highlight = base.transform_filter(brush)
  
  # layer the two charts & repeat
  alt.layer(
      background,
      highlight,
      data=source
  ).transform_calculate(
      "time",
      "hours(datum.date)"
  ).repeat(column=["distance", "delay", "time"])
  
subject: Update crossfilter to gray/blue scheme