https://learn.microsoft.com/en-us/uwp/api/windows.ui.xaml.media.animation.colorkeyframecollection.setat?view=winrt-28000
ColorKeyFrameCollection.SetAt(UInt32, ColorKeyFrame) Method (Windows.UI.Xaml.Media.Animation) -...
Sets the value at the specified index to the ColorKeyFrame value specified.
methodwindowsuixamlmedia