Honestly at this point my preference is to take the summarized taxon abundance tables produced by the script and import them into a different program to make my own bar charts -- if you want to make readable publication-quality images I think even something like Apple Numbers or Microsoft Excel can be made to work much better than fiddling with the matplotlib chart from Qiime.
However if you just want to change one or two colors with this file, you can find the relevant line and change the three-number color code. For example, here's one bacterium:
'k__Bacteria;p__Verrucomicrobia;c__Opitutae;o__Opitutales;f__Opitutaceae;g__Opitutus':('red232.119402985',(232,100,100)),
which you might want to change from red 232 / blue 100 / green 100 (a kind of greyish red color) to pure bright green (red 000, blue 000, green 255) you would change that line to:
'k__Bacteria;p__Verrucomicrobia;c__Opitutae;o__Opitutales;f__Opitutaceae;g__Opitutus':('red232.119402985',(0,0,255)),
Cheers,
-j