matplotlib.pyplot.draw()
…
This is used in interactive mode to update a figure that has been altered, but not automatically re-drawn. This should be only rarely needed, but there may be ways to modify the state of a figure with out marking it as stale. Please report these cases as bugs.

It appears that using Line2D.set_color does not cause matplotlib to re-render the figure. This means calling matplotlib.pyplot.draw() or fig.canvas.draw_idle() is required when changing the line color on a plot interactively.

• Matplotlib version, Python version and Platform (Windows, OSX, Linux ...)

  • Python version: 3.5.2
  • Matplotlib version: 1.5.3
  • Platform: Arch Linux 4.8.4 x86-64

• How did you install Matplotlib and Python (pip, anaconda, from source ...)

  • Both via pacman (Arch Linux package manager)

• If possible please supply a Short, Self Contained, Correct, Example that demonstrates the issue i.e a small piece of code which reproduces the issue and can be run with out any other (or as few as possible) external dependencies.

  import matplotlib
  import matplotlib.pyplot
  fig, [ax1, ax2] = matplotlib.pyplot.subplots(2)
  [line] = ax1.plot([0.0, 1.0], color="red")
  button = matplotlib.widgets.Button(ax2, "Greenify")
  def button_on_clicked(event):
      line.set_color("green")
      #fig.canvas.draw_idle()
  button.on_clicked(button_on_clicked)
  matplotlib.pyplot.show()

  1. Click the button. Avoid moving the mouse after clicking the button.
  2. Expected: The color should turn green. Actuality: It stays red. (It can turn green if you move your mouse, however.)

• If this is an image generation bug attach a screenshot demonstrating the issue.

• If this is a regression (Used to work in an earlier version of Matplotlib), please
  note where it used to work.