class_docstr: Generate color
class_docstr_tok: ["Generate","color"]
code: def emit(self, color=None):
      if color is not None:
          return color
      else:
          self.latest_auto_color += 1
          return "C{}".format(self.latest_auto_color)
  
file_path: adtk/src/adtk/visualization/_visualization.py
imports: import matplotlib.pyplot
  import numpy
  import pandas
  from pandas.plotting import register_matplotlib_converters
  from ..data import to_events, to_labels, validate_events
label_desc: Use image node_id 2 for calling the ColorGenerator obj's underlying member method code with example usage: obj.emit(color) and returns: color, str