Seeing as you have the macros in place for everything except the other sheet item, maybe all you'd seemingly need to do is put a condition in your macro if the formual contains an exclamation mark which is what a formula would have if it refers to another sheet.
In casual syntax:
Dim strFormula as String, cell as Range
strFormula = cell.Formula
If instr(strFormula, "!") > 0 then
'and at this point the formula does contain an exclamation,
'so induce the green color here