Glad Shooter41 started this thread. I don't have m... (
Those things you asked for are among the reasons why I advocate all manual and then shoot & chimp when dealing with flash. On a side note, in a (studio) setting, one may find the constant on lights to be easier to set-up and use.
If you find the flash too white for your preference:
-In JPEG setting, adjust the white balance in the camera.
-In RAW, adjust the white balance in post.
If you encounter and want to subdue a multiple cast light source, then use gel to filter/subdue unwanted color cast. Some scenes may benefit from polarizers.
Gel is good for film & for adjusting a scene which is lighted by different sources/colors of light.
The white balance in a digital camera allows us to adjust for the shade as we like. With film cameras, there is no in-camera white balance adjustment. That job is done with gels.
But if you encounter multiple shades of lighting striking your subject and wanted to control it, then the in-camera white balance may not be enough. What you can do is use a gel to filter the light to balance the scene or make it generally of one shade which can be easier to shift/adjust to something else at post.
To answer your question directly, aside from the exposure settings of the camera, that distance will depend on how powerful the flash was set and the modifier on the flash like zoom settings, reflectors, diffusers, bounce, etc. Personal knowledge & experience with situations and your gear would tell more.
Generally speaking, a "point" source of light will spread out and hit a surface. Imagine a candle lighting a wall. If we half the distance of the candle to the wall, we might expect the illumination to increase in half, and if we double the distance, the illumination to be decreased in half too. But not is not the case.
If we half the distance, the increase in brightness would be more than double, and if we increase the distance twice, the dimness would be more than half what we started with. This is due to the inverse square law that affects illumination.
We do not have to compute for these or dream of the mumbo jumbos. Make it simple, just keep in mind that the power and distance of light source will affect the amount of light reflecting on the subject. If the flash power setting is constant, close is more and away is less. Do a test shot then adjust the power of the flash or move the light closer or away as needed or desired.
We need to include the control of distance & position of our lighting in our shoot so the exposure would be consistent. If the photographer, in looking for a better composition and has a flash on his camera, steps forward, then expect the exposure to change, possibly overexposing the subject. The reverse is true if he steps back.
Parts of the subject getting near the light set-up will have similar effects. If somehow, she raises a hand and it comes near your lights, that hand will be more exposed.
Many other stuffs, gears, modifiers & settings can change the effect but I'm sure by the time you get to use those, you have mastered the basics well and it would not be of much trouble.