textBox1.Background = Brushes.Blue;
textBox1.Foreground = Brushes.Yellow;

WPF Foreground and Background 是System.Windows.Media.Brush. 您可以像这样设置另一种颜色：

using System.Windows.Media;

textBox1.Background = Brushes.White;
textBox1.Background = new SolidColorBrush(Colors.White);
textBox1.Background = new SolidColorBrush(Color.FromArgb(0xFF, 0xFF, 0, 0));
textBox1.Background = System.Windows.SystemColors.MenuHighlightBrush;