Fix plots that cause problems for people with protanomaly
For some wstudents with protanomaly, it is difficult to distinguish red from black. This is an issue for some plots used in the lecture notes, namely the following one in the notes about the nearly free electron model:
and plots B-E of graphene in the crystal structure notes:
Suggestion of the student: instead use colours with more contrast (like black and orange for example). Additionally, thicker lines might help (for the nearly free electron model plot).