Firstly, what does a key frame animation mean?
It is a way of specifying steps for your animation to follow.
The WPF runtime will work out the smooth transition between the steps for you.
Why would you want to do such a thing?
If you want to control how the animation flows, but don’t want to specify every point, then a key frame helps you.
In the following example, I have used a key frame animation to specify the periods at which the button’s rectangle changes colour.
It changes colour from AliceBlue to Blue to DarkGrey when you click on the button
Notice how you need to specify the target property as Fill.Color, if you don’t WPF tries complains that you are specifying a Color object when it is expecting a Brush!