You juste change link foreground color like that :
<StackPanel>
<TextBlock>
<Hyperlink x:Name="link" NavigateUri="http://www.microsoft.com">
View MS site !
</Hyperlink>
</TextBlock>
<Button Content="Change link colo" Click="Button_Click"/>
</StackPanel>
And in code behind :
private void Button_Click(object sender, RoutedEventArgs e)
{
Random r = new Random();
Color newColor = Color.FromRgb(
Convert.ToByte(r.Next(0, 255)),
Convert.ToByte(r.Next(0, 255)),
Convert.ToByte(r.Next(0, 255)));
link.Foreground = new SolidColorBrush(newColor);
}
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