title: Plotly express bar chart colour change
body: <p>How can I change the colour of the plotly express bar-chart to green in the following code?</p>
  
  <pre><code>import plotly.express as px
  import pandas as pd
  
  # prepare the dataframe
  df = pd.DataFrame(dict(
          x=[1, 2, 3],
          y=[1, 3, 2]
      ))
  
  
  # prepare the layout
  title = "A Bar Chart from Plotly Express"
  
  fig = px.bar(df, 
               x='x', y='y', # data from df columns
               color= pd.Series('green', index=range(len(df))), # does not work
               title=title,
               labels={'x': 'Some X', 'y':'Some Y'})
  fig.show()
  </code></pre>