code: def element_colors(element):
      
      keys = ['red', 'green', 'blue', 'alpha']
      candidate_colors = [element['data'][i]
                          for i in keys if i in element['properties']]
  
      if len(candidate_colors) >= 3:
          colors = np.column_stack(candidate_colors)
          signal = colors.ptp(axis=0).sum()
          return colors, signal
  
      return None, 0.0
docs: Given an element, try to extract RGBA color from
      properties and return them as an (n,3|4) array.
  
      Parameters
      -------------
      element: dict, containing color keys
  
      Returns
      ------------
      colors: (n,(3|4)
      signal: float, estimate of range