Change colours in 6.2: Axis manipulations

[ccamara]

It would be good if we manually forced the colours to be red and blue for Trump and Biden respectively, to allow better comparison and reduce cognitive dissonance.

Rationale

The notebook https://warwickcim.github.io/IM939_handbook/content/labs/Lab_6/IM939_Lab_6_2-AxisManipulation.html shows visualisations related to two political parties in the USA by using two plotting libraries: seaborn and altair and default colours, so students can compare how each library works.

1. The way they assign colours (and order lists) is different, so what orange and blue represent in each plotting library is different
2. Those political parties are usually associated to red and blue