code: def generate_vector_color_map(self):
          
          vector_stops = []
  
          # if join data specified as filename or URL, parse JSON to list of Python dicts
          if type(self.data) == str:
              self.data = geojson_to_dict_list(self.data)
  
          # loop through features in self.data to create join-data map
          for row in self.data:
              
              # map color to JSON feature using color_property
              color = color_map(row[self.color_property], self.color_stops, self.color_default)
  
              # link to vector feature using data_join_property (from JSON object)
              vector_stops.append([row[self.data_join_property], color])
  
          return vector_stops
docs: Generate color stops array for use with match expression in mapbox template