Private Sub Worksheet_Change(ByVal Target As Range)
Dim coul&, c As Range, n&
coul = [A1].Interior.Color
For Each c In UsedRange
If c.DisplayFormat.Interior.Color = coul Then n = n + 1
Next
Application.EnableEvents = False 'désactive les évènements
[C2] = n - 1
Application.EnableEvents = True 'réactive les évènements
End Sub