Set Foreground color for TextBlock
<Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="WPF" Height="160" Width="300"> <Grid> <TextBlock Foreground="DarkGray" VerticalAlignment="Center" HorizontalAlignment="Center" ToolTip="This is a custom tooltip" Text="Mouse Over for tooltip"/> </Grid> </Window>