Modify with a formula

hello to all

I have this question:

I have extracted the formula of the backgroundcolor of a field in a datawindow and I want to put it in my script with a modify.

but it doesn't  work.

Code extracted from the field in the DataWindow (it works)

>>    if ( campo2 < fido, rgb(255,0,0), if ( campo2 > ( abs(fido) * -1 ) and campo2 < abs(fido) , rgb(255,255,0), rgb(255,255,255) )  )

My script ( it does not work )

>>  ls_ = "campo2.Background.Color=if ( campo2 < fido, rgb(255,0,0), if ( campo2 > ( abs(fido) * -1 ) and campo2 < abs(fido) , rgb(255,255,0), rgb(255,255,255) )  )"

>>dw_stampa1.Modify(ls_)

what's wrong

thanks

Gimmy