Look in the Azeroth Grand Prix, it's open-source and it has a progress bar.
I would go with using 2 columns, both filled with "||||"s, with different colours of the text, and setting the column width according to the progress. ( f.e.: you have multiboard, that takes 10% of the screen width. for 50% progress, you set both columns to 5% of screen width. For 80%, you set the first to 8% and the second to 2%)