ColorsGenerator never returns random colors

[artygo8]

Describe the bug

ColorsGenerator never actually returns random colors.

Traceback (most recent call last):
  File "/home/arthurgossuin/code/gempy/z.py", line 6, in <module>
    next(color_iterator)
  File "/home/arthurgossuin/code/gempy/gempy/core/color_generator.py", line 69, in __next__
    result = self.hex_colors[self._index]
             ~~~~~~~~~~~~~~~^^^^^^^^^^^^^
IndexError: list index out of range

To Reproduce

Here is the content of the file used to produce the bug:

import gempy as gp

color_iterator = gp.ColorsGenerator()

for color in range(len(color_iterator.hex_colors) + 1):
    next(color_iterator)

Expected behavior

The code seems to imply that we should fall back on random colors once there are no colors left in hex_colors.

Screenshots

pass

Desktop (please complete the following information):

• OS: irrelevant
• GemPy Version
  • 3bf56a9

Additional context

As an ex geology student, and now fulltime software developer, I was intrigued by the library and started browsing the files when I found that bug. I would be happy to contribute further if you are open to it.