Just thought I'd share a quick comparison of expensive bulbs verses cheaper ones.
In this case; Osram Nightbreaker vs Ultra Xenon;
Ultras are on the left, Nightbreakers on the right.
To add to this I've found a very cheap supplier of Ultras: CLICKY
I can also confirm that the Ultras have been fitted for over 6 months and have not turned green and are still the same colour as they are in the photo.