Set background color of WPF Textbox in C# code

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

WPF Foreground and Background is of type System.Windows.Media.Brush. You can set another color like this:

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;

I take it you are creating the TextBox in XAML?

In that case, you need to give the text box a name. Then in the code-behind you can then set the Background property using a variety of brushes. The simplest of which is the SolidColorBrush:

myTextBox.Background = new SolidColorBrush(Colors.White);

I know this has been answered in another SOF post. However, you could do this if you know the hexadecimal.

textBox1.Background = (SolidColorBrush)new BrushConverter().ConvertFromString("#082049");

BrushConverter bc = new BrushConverter();

textName.Background = (Brush)bc.ConvertFrom("#FF7BFF64");

buttonName.Foreground = new SolidColorBrush(Colors.Gray);

Reference Here https://www.it-mure.jp.net/ja/c%23/c%EF%BC%83%E3%82%B3%E3%83%BC%E3%83%89%E3%81%A7wpf%E3%83%86%E3%82%AD%E3%82%B9%E3%83%88%E3%83%9C%E3%83%83%E3%82%AF%E3%82%B9%E3%81%AE%E8%83%8C%E6%99%AF%E8%89%B2%E3%82%92%E8%A8%AD%E5%AE%9A%E3%81%99%E3%82%8B/957683208/