text: Title: [DOCS] Colors tutorial
  Body: **Is your feature request related to a problem? Please describe.**
  
  Colors can use a full tutorial, due to issues like https://github.com/graphistry/pygraphistry/issues/241
  
  
  **Describe the solution you'd like**
  
  Cover:
  
  * Explicit colors: palettes, RGB hex
  * Symbolic encodings: categorical, continuous, defaults
  * Points vs edges
  * Linked from main docs + pygraphistry homepage
  
  
  **Describe alternatives you've considered**
  
  Current docs (code, readme) are not enough
  
  