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listBox1.ForeColor = System.Drawing.Color.Red;					

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private void listAnzeigen()
    {
      if (cVorzeichen == '-')
      {
        listEingaben.ForeColor = System.Drawing.Color.Red;
      }
      else
      {
        listEingaben.ForeColor = System.Drawing.Color.Black;
      }
    }					

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private void listBox1_DrawItem(object sender, System.Windows.Forms.DrawItemEventArgs e)
{
   // Set the DrawMode property to draw fixed sized items.
   listBox1.DrawMode = DrawMode.OwnerDrawFixed;
   // Draw the background of the ListBox control for each item.
   e.DrawBackground();
   // Create a new Brush and initialize to a Black colored brush by default.
   Brush myBrush = Brushes.Black;

   // Determine the color of the brush to draw each item based on the index of the item to draw.
   switch (e.Index)
   {
      case 0:
         myBrush = Brushes.Red;
         break;
      case 1:
         myBrush = Brushes.Orange;
         break;
      case 2:
         myBrush = Brushes.Purple;
         break;
   }

   // Draw the current item text based on the current Font and the custom brush settings.
   e.Graphics.DrawString(listBox1.Items[e.Index].ToString(), e.Font, myBrush,e.Bounds,StringFormat.GenericDefault);
   // If the ListBox has focus, draw a focus rectangle around the selected item.
   e.DrawFocusRectangle();
}					

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listBox1.DrawMode = DrawMode.OwnerDrawFixed;					

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    private void listEingaben_DrawItem(object sender, System.Windows.Forms.DrawItemEventArgs e)
    {
        // Create a new Brush and initialize to a Black colored brush by default.
        Brush myBrush = Brushes.Black;
  
        // Determine the color of the brush to draw each item based on the index of the item to draw.
          if (cVorzeichen == '-')
          { 
            myBrush = Brushes.Red;
          }
          else
          { 
            myBrush = Brushes.Black;
          }

        // Draw the current item text based on the current Font and the custom brush settings.
        e.Graphics.DrawString(listEingaben.Items[e.Index].ToString(), e.Font, myBrush,e.Bounds,StringFormat.GenericDefault);
        // If the ListBox has focus, draw a focus rectangle around the selected item.
      //  e.DrawFocusRectangle();
    }