CSHARP

color picker wpf

System.Windows.Forms.ColorDialog colorDialog = new System.Windows.Forms.ColorDialog();
 if (colorDialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
 {
      YourBtn.Background = new SolidColorBrush(Color.FromArgb(colorDialog.Color.A, colorDialog.Color.R, colorDialog.Color.G, colorDialog.Color.B));
      ColorName = colorDialog.Color.Name.ToLower();
 }

WPF color picker

// install Extended.Wpf.Toolkit

xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"

<xctk:ColorPicker Name="ClrPcker_Background" SelectedColorChanged="ClrPcker_Background_SelectedColorChanged"></xctk:ColorPicker>

private void ClrPcker_Background_SelectedColorChanged(object sender, RoutedPropertyChangedEventArgs<Color> e)
{
    TextBox.Text = "#" + ClrPcker_Background.SelectedColor.R.ToString() + ClrPcker_Background.SelectedColor.G.ToString() + ClrPcker_Background.SelectedColor.B.ToString();
}