The following code implements custom drawing of the fields inside datasources. It instructs to display field's alternate name if it's not empty; otherwise to display field name.

void queryBuilder1_FieldListDrawItem(Graphics g, Rectangle rect, DrawItemState state, MetadataField field, ref bool handled)
{
       Brush bgBrush;
       Color textColor;
       String s = String.Empty;

       if ((state & DrawItemState.Selected) == DrawItemState.Selected)
       {
               bgBrush = SystemBrushes.Highlight;
               textColor = SystemColors.HighlightText;
       }
       else
       {
               bgBrush = new SolidBrush(Color.LightYellow);
               textColor = Color.MediumSeaGreen;
       }

       rect.X -= rect.Height;
       rect.Width += rect.Height;

       g.FillRectangle(bgBrush, rect);

       if (field != null)
       {
               if (!String.IsNullOrEmpty(field.AltName) && queryBuilder1.UseAltNames)
               {
                       s = field.AltName;
               }
               else
               {
                       s = field.Name.QualifiedNameWithoutQuotes;
               }
       }
       else
       {
               s = "*";
       }

       TextRenderer.DrawText(g, s, new Font("Arial", 8, FontStyle.Bold), rect.Location, textColor);

       if ((state & DrawItemState.Focus) == DrawItemState.Focus)
       {
               ControlPaint.DrawFocusRectangle(g, rect);
       }
       handled = true;
}