Patch brown color and legend geometry placement

[banesullivan]

For some reason the color brown was mapped incorrectly in colors.py... previously it was red-ish.

Also, some markers in the legend would not always be placed correctly becuase they need to be centered at (0,0) - this fixes that

import pyvista as pv
from pyvista import examples

p = pv.Plotter()
p.add_mesh(examples.download_bunny(), label="mesh", color="brown", lighting=False)
p.add_legend()
p.show()

now we get

---

Previously misplaced legend markers:

which are fixed to

[akaszynski]

colors.py was originally just copied from the matplotlib source, so I'm surprised it wasn't correct since I don't recall brown not being mapped properly.

Thanks for fixing this.