was told the white one was pressed into service a little more quickly than planned (ie. before the proper paint job) to replace the one that got 'punctured' by it's jack. I could of course be totally wrong.
The white MD belongs to Safair and is leased to them including ground support/maintenance etc.
Possibly introduced to increase the seating capacity per sector, as well as shortage due to DC9 jack incident.
Rumour gas it that the DC9 that got a "jack-up-its-rear-end" will in fact be repaired fully.