I've started using the Natural Color System, https://en.wikipedia.org/wiki/Natural_Color_System, for my matplotlib visualisations. Snippet of code I use on categorical data:

  good_patch = matplotlib.patches.Patch(color='#009F6B', label='good')
  marginal_patch = matplotlib.patches.Patch(color='#FFD300', label='marginal')
  warning_patch = matplotlib.patches.Patch(color='#FF751F', label='warnings')
  bad_patch = matplotlib.patches.Patch(color='#C40233', label='bad')
  flag_patch = matplotlib.patches.Patch(color='#0087BD', label='flag')
  unknown_patch = matplotlib.patches.Patch(color='#808080', label='unknown')