They should have checked the flow of the injectors first to make sure they are a balanced set.
The design of the inlet will cause a slight difference in fuelling, but not normally enough to matter, the main thing though that causes the difference is the WATER PUMP, or rather it's location relative to the cylinders, the nearest one receiving the best cooling, on to the furthest one getting hotter than the others as water has heated on the way through past the other cylinders.
I always check the injectors if there is one slightly higher I put that in no4, slightly lower will go no1 etc.
It does look v white, but may just be running very clean, hard to tell from piccie, I think just replace and you'll be ok, but I would get a full load fuelling check done asap.
What plugs are they by the way ?, a HG on the way out can do some odd things, had that before melted the earth electrode, but also turned the plug green!!
tabetha