Animination: Excel Chart Bar

[Apple111]

Using PPt 2007, I seldom use animation in Powerpoint.

I would like to know how do I grey out some portions of a bar chart.

Attached a sample.

1) How do I grey out the first 3 sets of bars on the left?

2) How do I grey out the first 3 bars in each set?

1) and 2) are separate animations that are done on separate charts.

Thank you