在DBGrid的OnDrawDataCell事件下写：
procedure TForm1.DBGrid1DrawDataCell(Sender: TObject; const Rect: TRect;
  Field: TField; State: TGridDrawState);
begin
  if Table1.FieldByName(''partno'').AsFloat > 2500 then
  DBGrid1.Canvas.Brush.Color := clGreen;
  //DBGrid1.Canvas.Font.Color := clRed;
  DBGrid1.DefaultDrawDataCell(Rect, Field, State);
end;

或(注意是"或")在OnDrawColumnCell下写：

二者的区别是OnDrawDataCell必须是Columns属性为csDefault，既为空。而OnDrawColumnCell没这个要求。

procedure TForm_cost.DBGrid1DrawColumnCell(Sender: TObject;
  const Rect: TRect; DataCol: Integer; Column: TColumn;
  State: TGridDrawState);
begin
  with DBGrid1 do
    begin
      if ((State = [gdSelected]) or (State=[gdSelected,gdFocused]))     then
      begin
        Canvas.Font.Color :=clLime;
        Canvas.Brush.Color :=clMaroon;
      end
    else
      if Table1.FieldByName(''Salary'').AsFloat < 40000 then
begin
canvas.Font.Color := clYellow;
canvas.Font.Style := [fsItalic];
Canvas.brush.Color := clGreen;
end
else
begin
canvas.Font.Color := clNavy;
Canvas.Font.Style := [fsBold];
Canvas.brush.Color := clRed;
end;
DefaultDrawColumnCell(Rect, DataCol, Column, State);
end;
//DBGrid1.DefaultDrawColumnCell(Rect, DataCol, Column, State);
end;