求教，如何使行的背景色随数字的变化交替变化

* 用颜色显示不同分数的行
PUBLIC oForm
oForm = NEWOBJECT("Form1")
oForm.Show
Return

DEFINE CLASS form1 AS form
    DoCreate = .T.
    AutoCenter = .T.
    Caption = "Form1"
    Name = "form1"
    ADD OBJECT grid1 AS grid WITH ;
        Height = 228, ;
        Left = 12, ;
        Top = 12, ;
        Width = 348, ;
        Name = "Grid1"
    PROCEDURE Init
        * 生成测试临时数据表
        Create Cursor Cj (编号 C(4),总分 N(3))
        =Rand(-1)
        For lnI=1 To 50
            Insert Into Cj Values (Padl(lnI,4,"0"),Rand()*100)
        EndFor
        * 结束
        Go Top
        With ThisForm.Grid1
            .RecordSource="Cj"
            .SetAll('DynamicBackColor','iif(总分>=90,Rgb(255,0,0),Iif(Between(总分,60,89),Rgb(0,128,0),Rgb(255,0,255)))','Column')
        EndWith
    ENDPROC
ENDDEFINE