How to customize the legend in Google Chart?

Question

Hi,

I need to specify labels (and associated colors) of a legend NOT in the same order as my data sets.

Actually I have only one data set but I display my bar chart with 2 colors.

Indeed, my dataset is an ordered value score associated to a person. If this person is from Group1, then the bar is displayed in blue otherwise it is displayed in green.

Here is an example of my url:

http://chart.apis.google.com/chart?cht=bhg&
chd=t:100,93,100,80,70,27&
chco=00FF00| 00FF00 |0000AA|0000AA|0000AA|00FF00&
chdl=Group1|Group2

Now how do I display a legend with two labels with 2 colors that refer to the same colors above??

Thx

PS: I tried to add color for 2 "virtual" datasets like this chco=00FF00| 00FF00 |0000AA|0000AA|0000AA|00FF00, 00FF00, 0000AA but the chart displays 3 legend labels (with 3 colors !!)