请问在dbchart中画线时,怎样实现大于零 的数值以蓝色线条表示,小于零的数值以红色线条表示?

with       adoquery_sum   do 
                            begin 
                              dbchart.Series[0].Clear; 
                              while       not       adoquery_sum.eof           do 
                                    begin 
                                    if     adoquery_sum.FieldValues['BudgetVariance']> 0     then 
                                    begin 
                                    dbchart.Series[0].Add(   adoquery_sum.FieldValues['budgetvariance'],adoquery_sum.FieldValues['date'],clblue)   ; 
                                    end 
                                    else 
                                      dbchart.Series[0].Add(   adoquery_sum.FieldValues['budgetvariance'],adoquery_sum.FieldValues['date'],clred); 
                                      adoquery_sum.next; 
                                      end; 
                            end;   


这样写好像也没有用啊   ??