The difference between yellow and gray arrows, besides their colors, are their sense of being.
I believe the gray arrow is for people getting of the train while the yellow is for passengers standing in line, waiting till they can enter the vehicle.
The reason behind is to avoid red head pips and series of unfortunate events.
UNFORTUNATELY, it seems that most of us have different interpretations of such arrows.
Meaning? TAX WASTED.
My suggestion would be bigger trains like LRT 2 instead of bigger signage's that might be making other pocket big.
Change will never be effective if the one feeding it can never even swallow change.