Changing background colour for alcoves in root system

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I want to draw a 2d affine root system with some alcoves highlighted, preferably by giving them a different background colour.

Here is an example:

# def root system
Phi = RootSystem(["A",2,1]).ambient_space()

# plotting 'background' root system
plot_background = Phi.plot(fundamental_chamber=True,roots=False,coroots=False,\
                           fundamental_weights=False,)

# defining alcoves to be highlighted
W = L.weyl_group()
S = W.simple_reflections()
alcoves = [S[0],S[1],S[2]]

# plotting 'highlighted' alcoves
plot_alcoves = Phi.plot(fundamental_chamber=False,roots=False,coroots=False,\
                        fundamental_weights=False,reflection_hyperplanes=False,\
                        alcoves=alcoves,alcove_labels=True)

# show plot
(plot_background + plot_alcoves).show(frame=False, axes=False)

Now, I would like the 'labelled alcoves' to have a different background colour. Is that possible?

I can't find anything in 'Tutorial: visualizing root systems' nor the docu for plot() in 'Root lattice realizations'. (Sorry for not posting links, apparently my karma is insufficient for that as a new user.)

Thanks for suggestions!