[Bug]: User Warning during boxplot creation

[myrmarachne]

Environment

- QF-LIB: 3.0.0
- Python: 3.11

What happened?

Creation of boxplots raises the following User Warning:

UserWarning: The palette list has more values (4) than needed (1), which may not be intended.
  sns.boxplot(ax=self.axes, data=self._data, palette=palette, **plot_kwargs)

Screenshots

No response

Reproduction steps

Run the return_quantiles_chart.py demo script and you can observe the warning.

Relevant log output

No response