Black title changes colour when exporting MXF ???
Might be an issue with the smart rendering option available for MXF in Premiere/AME.
Try disabling that.

http://blogs.adobe.com/kevinmonahan/2012/10/11/smart-rendering-in-premiere-pro-cs6-6-0-1-and-later/

If that doesn't work. Render an intermediate and re-import and encode that to MXF.
Though keep in mind that MXF is just a container, you have different codecs available.
Make sure you choose the one suitable for your source footage and what your client requested.