Excel - Style format on drop down list selection - excel

Question

I'm working on a excel document being generated with APACHE POI.
The document is filled with many drop down lists for data validation.
The data chosen in those drop down lists are always of the same type:
LABEL (ID)
For the person who fills the excel document, the ID is less important than the LABEL _ but the ID is still necessary for parsing purposes.
I managed through APACHE POI to put a specific format on those kind of cells, in order to help the user to focus on the information more useful to him/her :
LABEL is in black
(ID) is in grey
My problem: when the user change a value in the cell throught the drop down list, the style format is lost on the cell.
My question: is it possible to set up a listener on my excel document that does the folowing job:
on ANY cell
filled through ANY drop down list
on ANY sheet of the workbook
set the specified cell format ?
I already have a function that does the "style format" job, but I don't know how to plug it on this kind of listener...
Function formatStyle()
Dim cellContent As String
Dim valeurLength As Integer
For Each currentCell In Selection.Cells
cellContent = currentCell.Value
For valeurLength = 1 To Len(cellContent)
If Mid(cellContent, valeurLength, 1) = "(" Then
Exit For
End If
Next valeurLength
With currentCell.Characters(Start:=1, Length:=valeurLength - 1).Font
.ThemeColor = xlThemeColorLight1
.TintAndShade = 0
End With
With currentCell.Characters(Start:=valeurLength, Length:=Len(cellContent) - valeurLength + 1).Font
.ThemeColor = xlThemeColorDark1
.Color = -4144960
End With
Next
End Function

Answer 1

Excel Form controls don't support any kind of font and color formatting. ActiveX controls let you change the font and colors, but not of individual characters. Custom drawing parts of the control most likely can be achieved with some complicated VBA and WinAPI calls.
The closest alternative I can think of is some of the bold extended Unicode characters:

Answer 2

Thanks to Determine if cell contains data validation, I've managed to do exactly what I wanted:
Private Sub Workbook_SheetChange(ByVal Sh As Object,ByVal Target As Range)
Dim cell As Range, v As Long
For Each cell In Selection.Cells
v = 0
On Error Resume Next
v = cell.SpecialCells(xlCellTypeSameValidation).Count
On Error GoTo 0
If v <> 0 Then
formatReferenceCell (Target)
End If
Next
End Sub
Function formatReferenceCell(cellContent)
Dim X As Integer
For X = 1 To Len(cellContent)
If Mid(cellContent, X, 1) = "(" Then
Exit For
End If
Next X
With ActiveCell.Characters(Start:=1, Length:=X - 1).Font
.ThemeColor = xlThemeColorLight1
.TintAndShade = 0
End With
With ActiveCell.Characters(Start:=X, Length:=Len(cellContent) - X + 1).Font
.ThemeColor = xlThemeColorDark1
.Color = -4144960
End With
End Function