title: How to set a colour legend with the days of the week in Plotly bar chart
body: <p>i have a graph like this: <a href="https://i.stack.imgur.com/WWrSx.png" rel="nofollow noreferrer">https://i.stack.imgur.com/WWrSx.png</a>
  and i would like to have a legend with the name of the days of week, each of them with their own color
  so that every bar in the chart ( which represent a single day) have his respective colour associate with the day of the week.
  I hope i have been understendable, thanks a lot to everyone who'll reply.</p>