User Defined Global Formula with Tally Default Fields

Dear All
I have done a simple form with
[System : Formulas]
SysFormula1 : $$LocaleString:#FirstFieldName
SysFormula2 : $$LocaleString:#SecondFieldName

Above working fine with my form, but i want to use with tally default fields DSP VchDate
[#Field : DSP VchDate]
Set As : @@SysFormula1
Width : SysFormula2
But Not getting result, plz. guide. Thanks

 

Dear Sir,
As a learner, Can't understand your code,
I have New Form storing string value (Say Field1 Set As : "Green" for current company)
Also Declared System Formula.
Now Modify Tally Default Field
[#Field : DSP VchDate]
Background : @@Field1 ;; Not getting plz. help again.

 

Dear Sir,
Please explain