How change the graphic bar´s color using macro ?

Hi,

In my presentation I have some slides containing graphics. The data sheet
for each graphic is linked to an excel range.

I would like to change the graphic bar´s color according value shown (e.g:
if value < 50 the bar must be red, if >= 50 the bar must be green).

Is there some way to do this using macro (vba) ? How can I do this ?

Thanks in advance.

Jerry - Brazil