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();
}