System.Drawing.Color

TextBox1.BackColor=System.Drawing.ColorTranslator.FormWin32(RGB(164,196,255))
or
TextBox1.BackColor=System.Drawing.ColorTranslator.FormHtml("#ff00ff")
or
TextBox1.BackColor = System.Drawing.ColorTranslator.FromHtml(Select1.Value)
or
TextBox1.BackColor = SystemColors.Control
TextBox1.BackColor = Color.Red
TextBox1.BackColor = Color.FromKnownColor(KnownColor.Control)