If you want a property of your gauge to be one solid color, apply the Solid brush element to the property.
To apply the Solid brush element to a property of your gauge at design time:
Add a Radial Gauge to the Gauges collection.
In the left-hand pane of the Gauges collection editor, click Radial Gauge.
Expand the Dial property.
From the BrushElement drop-down list, select Solid Fill. This will create a new Solid Fill brush element.
Expand the newly created BrushElement property, and locate the Color property.
Set the Color property to Black.