Allow specifying a color for simulator reflectors

[hakonanes]

Description of the change

This PR enables passing a valid Matplotlib color to color simulator reflectors in KikuchiPatternSimulator.plot() when plotting with Matplotlib (not PyVista).

This is useful when you want to plot more than one phase's reflectors in the same (stereographic) plot, coloring one red and one blue, e.g.

Also, contrast with linear or square scaling (of intensities from structure factors) is improved.

Progress of the PR

• [x] Docstrings for all functions
• [x] Unit tests with pytest for all lines
• [x] Clean code style by running black via pre-commit

Minimal example of the bug fix or new feature

>>> from diffsims.crystallography import ReciprocalLatticeVector
>>> import kikuchipy as kp
>>> mp_si = kp.data.si_ebsd_master_pattern(allow_download=True, lazy=True)  # Get Si phase
>>> rlv = ReciprocalLatticeVector(mp_si.phase, hkl=[[1, 1, 1], [2, 2, 0], [4, 0, 0]])
>>> rlv = rlv.symmetrise()
>>> rlv.sanitise_phase()
>>> rlv.calculate_structure_factor()
>>> simulator = kp.simulations.KikuchiPatternSimulator(rlv)
>>> simulator.plot(color="r")

For reviewers

• [ ] The PR title is short, concise, and will make sense 1 year later.
• [ ] New functions are imported in corresponding __init__.py.
• [ ] New features, API changes, and deprecations are mentioned in the unreleased section in CHANGELOG.rst.
• [ ] New contributors are added to release.py, .zenodo.json and .all-contributorsrc with the table regenerated.