Thanks Trey,
Looking at your code, I came up with:

FOR EACH oCol IN THISFORM.Ipageframe1.Page1.grdAsso.COLUMNS

IF oCol.ColumnOrder%2 = 0
oCol.BACKCOLOR = 16711622 &&-Light Blue
ENDIF
ENDFOR

in the INIT of the form. Works fine!

Thanks again,
Julian