New Post: Change Highlight/Select Color of NumericUpDown

Hi,

I believe you are talking about the Background color when the mouse is selecting the numeric values, inside the DoubleUpDown.
For a TextBox, you would use :

SelectionBrush="Red"

For a DoubleUpDown, you can create your own DoubleUpDown, and set its TextBox's SelectionBrush :

 public class MyDoubleUpDown : DoubleUpDown
  {
    public override void OnApplyTemplate()
    {
      base.OnApplyTemplate();
      if( this.TextBox != null )
      {
        this.TextBox.SelectionBrush = Brushes.Red;
      }
    }
  }