You could change the Infragistics wrapper code. The IBusinessBindable interface forces a property named BindingEditable to be implemented on the control. At the moment, the Infragistics wrapper just sets the enabled state of the control. You can add the code here to change the disabled color as well.
Public Property BindingEditable() As Boolean Implements IBusinessBindable.BindingEditable
Get
Return Me.Enabled
End Get
Set(ByVal value As Boolean)
Me.Enabled = value
If Not value Then
'-- Set the disabled color text here
End If
End Set
End Property