so, you had a gradient stroke here, it made the stroke look really bad against a dark BG and .. well basically it was unneeded
remove gradient stroke
I think that gradient trick is still needed here, you can use it to add a nice looking inner shadow to the Donut.
You are right that it might now always work on dark backgrounds. That's why I've added shadowColor option to Donut in new version where you can define it.
right you can* use it, why not just allow the user to pass a gradient if they want to.. like this code allows for
Got your point. Added option called generateGradient that is turned off by default (so you can use any fill you like) but can be use to automatically generate shadow gradient.