I've done T-5, 4-tube low-bays before and I seem to remember the white & grey ballast lead connected together at the factory with a push-in connector and a lead coming off to connect to the neutral of the supply
Is this correct?
I saw another brand that has black, white and gray, but they show the supply neutral connected to the white ballast lead, and also feeding a switch that connects the grey lead to the whites.
although have installed a bunch of them I never looked inside at the ballast(s) until recently these 4 light Stoncos use a three lamp and single lamp ballast, which makes switching inside/outside impossible... so I am no help
I just assumed the electronic ballasts had no color code standards
I was actually stunned at the replacement cost of the three lamp unit..>$90
Working from a rather feeble memory, if you connect the grey wire to the neutral (and possibly the hot) all 4 lamps will come on when power is applied to the fixture. The gray can be run through a motion sensor or other control device to provide dual level lighting.
Few things are harder to put up with than the annoyance of a good example.
I have installed these fixtures before and yes it is to be able to switch 2 or 3 of the lamps independently.. WHY they choose to do this with the neutral puzzles me, but as far as I know and have read, this is the purpose of the grey wire.
I think perhaps it is intended for some sort of optional "occupancy sensing" system, where 1 or 2 out of 4 lights normally burn constantly but the remaining lamps are fired up when a person or object moves in the area below the fixture.