Thank you so much John!! It is clunky but at least it works (what I have not been able to so far)! I have customized it so it changes the typed text to red when it is black and vice versa. Maybe there's sth to do it in a "cleaner" way by sort of selecting the character after where you are typing. Although don't know how if you are at the end of your textbox.
For reference my code:
Sub redfont()

Set otxr2 = ActiveWindow.Selection.TextRange2
Dim lettre_avt As Integer

If (Not otxr2 Is Nothing) Then
    If otxr2 = "" Then
        lettre_avt = ActiveWindow.Selection.TextRange2.Start - 1
        If ActiveWindow.Selection.ShapeRange.TextFrame.TextRange.Characters(lettre_avt).Font.Color.RGB <> 0 Then
            'type black
            otxr2.InsertAfter ("A")
            otxr2.Font.Fill.ForeColor.RGB = vbBlack
            SendKeys "{BKSP}"
        Else
            'type red
            otxr2.InsertAfter ("A")
            otxr2.Font.Fill.ForeColor.RGB = vbRed
            SendKeys "{BKSP}"
        End If
    End If
End If

End Sub