A few options, depending on where you might head next:
Option 1: By default, bar is going to use the ColorOrder from the axes for its colors, and the values repeat themselves. The default colororder has 7 colors and you have 6 bars, so using 6 colors would do the trick here:
Option 2: The way ColorOrder maps colors uses the SeriesIndex property. The first 6 bars have SeriesIndex values of 1 through 6, the second have values 7-12. This means you can keep your ColorOrder as it was, and if you added a line (for instance) it would use the 7th color.
b2(i).SeriesIndex = b1(i).SeriesIndex
Option 3: You could just set the FaceColor directly. Be careful with this one as it means that future calls to colororder will affect b1 (which is still using automatic colors) but not b2.
b2(i).FaceColor = b1(i).FaceColor;