The white balance

Don’t OpenMV need to turn on white balance when working?
What functions require white balance gain?
Or what kind of environment needs to be turned on?

White balance is on by default for the camera modules. You should turn it off for color tracking. If white balance is not used the image colors will look off given the environment.

Do you have to turn off the white balance when looking for color blocks?
For example, does openmv have to be on white balance to run in a factory?

Yes, just do:

sensor.set_auto_white_bal(False)

Immediately after resetting the sensor.

http://docs.openmv.io/library/omv.sensor.html?highlight=white%20balance#sensor.sensor.set_auto_whitebal

How far does the Apriltag feature recognize?

Depends on the tag size relative to the camera. An 8"x8" tag is about 8ft.