Accurate color mixing in Matplotlib-Venn

With the following code:

from matplotlib import pyplot as plt
from matplotlib_venn import venn2
from collections import OrderedDict

named_sets = {'x1': set(['foo','foo','bar',"pax"]), "x3" : set(['foo','qux','bar',"zoo"])}
od = OrderedDict(sorted(named_sets.iteritems()))

circlenm = ()
circlels = []
for k,v in od.iteritems():
    circlenm = circlenm + (k,)
    circlels.append(v)


c = venn2(subsets = circlels,set_labels = circlenm)
c.get_patch_by_id('10').set_color('red')
c.get_patch_by_id('01').set_color('blue')
c.get_patch_by_id('10').set_edgecolor('none')
c.get_patch_by_id('01').set_edgecolor('none')
c.get_patch_by_id('10').set_alpha(0.4)
c.get_patch_by_id('01').set_alpha(0.4)
plt.show()

      

        
        
        
      

    

I can get the following figure:

Here I would like to combine the "blue" circles with the "red" ones. Note that the mixing result is brown .

But the actual value should be light magenta (the picture below is generated by default matplotlib_venn.venn3

):

How can I achieve this correctly?