help with colors and bar()

Hi! I red that plotting multiple dataset would cause matplotlib to automatically cycle all available colors.
This seems not to be the case with the bar() function, used to plot bar graphs.
If i try, eg:
a=array([1,2,3])
b=array([1,0.8,1.1])
bar(a,b)
bar(a*0.9,b*0.9)
show()

I'll get the two plots superimposed but all of the same color (blue).

I have also another problem: whichever color I set for the bars, the bars' border is always black. So it is impossible to have a global idea of the plotted data because at a little magnifing ratio every bar is black! How can I set the border of the bars to another color (best white)?

Thanks!