Rear bearings, green vs timken

My Ford E-250 (2010) still uses Timkens, but The GM's run greens. Sounds right? thats what my fleet mechanic told me. I have had a sealed bearing failure in my Breeze, front hub went south, squealed and then cooked. had to buy an entire hub from junyard which was cheaper than the new bearing anyway and lasted me another 40K until I junked it. I dont think they are meant to even be serviced.