title: Openpyxl: use excel theme colors in chart
body: <p>I'm trying to use Excel's theme colors in a chart created by openpyxl.  I want to have theme colors so that the entire workbook's colors can be updated when the user loads a new theme.</p>
  
  <p>Openpyxl has functionality to color the series bars in a bar chart with rgb values as shown below.</p>
  
  <pre><code>import openpyxl
  wb = openpyxl.load_workbook('myBook.xlsx')
  ws = wb["chartSheet"]
  chart = openpyxl.chart.BarChart()
  chart.type = "col"
  data = Reference(ws, min_col=2, min_row=1, max_row=7, max_col=3)
  cats = Reference(ws, min_col=1, min_row=2, max_row=7)
  chart.add_data(data, titles_from_data=True)
  chart.set_categories(cats)
  
  
  chart.series[0].graphicalProperties.solidFill = 'FFFF66'
  
  
  ws.add_chart(chart, "B2")
  </code></pre>
  
  <p>For styling the fill color of a cell, there is an <a href="https://openpyxl.readthedocs.io/en/stable/api/openpyxl.styles.colors.html" rel="nofollow noreferrer">openpyxl.styles.colors.Color</a> object that allows you to define colors in terms of a theme, like this: <code>openpyxl.styles.colors.Color(theme=7)</code></p>
  
  <p>However, the object that is used for bar chart styling is an <a href="https://openpyxl.readthedocs.io/en/stable/api/openpyxl.drawing.colors.html" rel="nofollow noreferrer">openpyxl.drawing.colors</a> object which only accepts rgb values.</p>
  
  <p>It's definitely possible within the Excel application to style bars with a theme color.  Theoretically, I could use some post-production script to edit the raw xml of the excel file after being saved, but that would be pretty inefficient.</p>
  
  <p><strong>Is there any way to accomplish this within openpyxl?</strong> </p>