I bought a green F28T12 yesterday, and I've been unable to turn it on. There's some blackening around one side of the electrodes, but I can still measure continuity across it.
I've tried both preheat and electronic ballasts with no luck. With preheat there's literally nothing, whereas with electronic (instant start I presume), the side with blackening glows a very mild green without any discharge being formed.

Is there any way to get it to work? It's supposedly a new lamp but it's completely generic with nothing but a G marked on it.

May be the tube has leaked? Do you have a source of high frequency high voltage like a tube checker or just a plasma globe to check if the fill is still OK?

Sounds like it has some sort of contamination

The tube works but won't strike. I don't have a lamp tester yet, but using a "400kV" (around 15kV) HV converter I'm able to see it glow a dim green.
My test was between two opposite terminals so it won't confirm filament strength and such but the lamp doesn't have vacuum loss.