Well sunlight provides everything in the spectrum (cool and warm and everything in between) so in it's natural setting, it is switching from USING the blue even though the red is there too for vegging, and then as it flowers it switches to USING mostly the red spectrum even though the blue is still there. Comparing natural sunlight to inside grow rooms lights is pointless. Just because you see no difference in light outdoors doesn't mean the plant is using the same spectrum the whole time....
If you look around you will find that it is very possible to grow from seed to finish with the warm spectrum only, regardless of whether it's an auto or not. However if you try to use the cool spectrum the whole grow the flowers will be TINY and the plant will be leggy...