.
.
Paste this code in the ThisWorkbook module :
Option Explicit
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
If Target.HasFormula Then
Target.Interior.Color = vbRed
Else
' remove background colour entirely (i.e. No Fill)
Target.Interior.ColorIndex = xlColorIndexNone
End If
End Sub
It checks all cells throughout the workbook for the EQUAL symbol. If the symbol is present, it colors the cell RED.
You can change the "Target.Interior.ColorIndex = xlColorIndexNone to the commands for formatting the cell.