How to creat multi color bar legend

Hi all,

I am doing a project where I am looking at some inventory values, where there is both positive (color green) and negative (color red) values.

How do I make the legend for this data set both colors ?

By default my excel (2010) sets the legend to green, but right now I only have negative values (red) which makes the legend look kinda weird, because there isn't any green bars in the graph. The question is basically how to make the legend half green/ half red.

Hope you guys can understand my problem and help me

Br,
Simon.