Change the forecolor setting to the backcolor setting and then back to black e.g.

Private Sub CheckBox1_Change() 
    With Me 
        If .CheckBox1.Value = True Then 
            .TextBox1.Enabled = True 
            .TextBox1.BackColor = &H80000005 
            .TextBox1.Forecolor = &H80000012
        Else 
            .TextBox1.Enabled = False 
            .TextBox1.BackColor = &HE0E0E0
            .TextBox1.Forecolor = &HE0E0E0
        End If 
    End With 
End Sub