Пример OwnerDraw для Listbox

procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer;
  Rect: TRect; State: TOwnerDrawState);
var
  S: string;
  N: Word;
  WasColor: TColor;
begin
  with Control as TListBox, Canvas do
  begin
    S := Items[Index];
    FillRect(Rect);
    MoveTo(Rect.Left + 2, Rect.Top);
    SetTextAlign(Canvas.Handle, TA_LEFT or TA_UPDATECP);
    WasColor := Font.Color;
    for N := 1 to Length(S) do
    begin
      case UpCase(S[N]) of
        'A', 'E', 'I', 'O', 'U': Font.Color := clRed;
      else
        Font.Color := WasColor;
      end;
      WinProcs.TextOut(Canvas.Handle, 0, 0, @S[N], 1);
    end;
  end;
end;