Sub Changer_couleur()
Dim r As Range
Dim i As Integer
For Each r In Range("A1:A" & Range("A1").CurrentRegion.Rows.Count)
For i = 1 To Len(r.Value)
If r.Characters(Start:=i, Length:=1).Font.Color <> vbRed Then
r.Characters(Start:=i, Length:=1).Font.Color = vbBlue
End If
Next
Next r
End Sub