Gradient Fill Problem - Doughnut Chart

I'm trying to make a "speed dial" background to use for a performance evaluation dashboard. I need to have a red-to-green "path" gradation around the 3/4 wedge doughnut upon which I'll superimpose a dial to indicate performance. I've played with the various gradient fill tools but am thus far unable to create a background where the color gradation is constant (in terms of chroma & hue) from the inside to the outside. Has anyone been able to overcome this before? Or, do I need to create this in a graphics program and insert it as an image? Please see attached file for illustration. Thanks for your advice. David