Here's one way - you'll need to add the skeleton handlers from the Properties Box to ensure the MouseEnter and MouseLeave events are wired up:
private void button1_MouseEnter(object sender, MouseEventArgs e)
{
button1.Foreground = Brushes.Red; // say
}
private void button1_MouseLeave(object sender, MouseEventArgs e)
{
button1.Foreground = Brushes.Black; // or whatever it was to start with
}