Animating the color of a line in WPF
1) I believe it is not a good practice to give variables one-letter names. Storyboard story = ...
2) I believe you can specify Duration in ColorAnimation only. And do not set it for Storyboard.
3) I would introduce variable for ColorAnimation because s.Children[0] looks weird to me when I know that it is ColorAnimation.
4) Strangely you are using 0.1f where parameter is double anyway.
5) I would consider using object and collection initializers for Storyboard.Children.
6) Optionally I would think on removing storyboard variable and start it immediatly after constructing.

Result: my code looks differently, but readability changes are subjective:  

Line TargetLine = line;

var duration = new Duration(TimeSpan.FromSeconds(0.1));
var colorAnimation = new ColorAnimation(Colors.LightGreen, duration);
Storyboard.SetTarget(colorAnimation, TargetLine);
Storyboard.SetTargetProperty(colorAnimation, new PropertyPath("Stroke.Color"));

new Storyboard {Children = {colorAnimation}}.Begin();