Add a property lSw and a method ChangeSw to your form.

*ThisForm.ChangeSw

With This
    .lSw=Not .lSw
    return .lSw
EndWith

*ThisForm.YourGrid.Init - for a chess pattern

This.SetAll("DynamicBackColor", "iif(ThisForm.ChangeSw(),"+lcColor1+","+lcColor2+")", "Column")

*ThisForm.YourGrid.Init - for a jail pattern

For each col in This.Columns
    col.DynamicBackColor=iif(mod(col.ColumnOrder,2)=0, ;
          "iif(ThisForm.ChangeSw(),"+lcColor1+","+lcColor2+")", ;
          "iif(Not ThisForm.ChangeSw(),"+lcColor1+","+lcColor2+")")
EndFor

I leave the rest to you. Do not forget to instantiate lcColor1 and lcColor2.

Later edit: I forgot to mention there is a catch: a small bug(caused by scrooling in VFP7 with sp1) that make sometimes that only 2 adiacent rows in jail pattern to have the same color.