Partially transparent scatter plot, but with a solid color bar

Alright, I found one way to do it, that looks relatively clean: (using the ColorBar object from the question)

color_bar.set_alpha(1)
color_bar.draw_all()
# pylab.draw() or pyplot.draw() might be necessary

It would be great to get a confirmation that this is the most robust way to proceed, though! 🙂