as far as I'm aware, the 2D gauge color scheme is fixed and will change depending on the ratio <CurrentValue> : <MaxValue - MinValue>.
There were some discussions going on to make it more customizable in the future.
For getting the attributes I mainly work with the Developer Tools in the browser for the preview and "Inspect" a certain element. But in the end, I'm using the "Class" property to define my own class in the "Application Styles".
I hope that helps...