While making a portrait in a home or office with a common flash, turn off or dim most of the lights. This eliminates stray, off-color light from reflecting from the subject and keeps the color balance to only the light emitted from the flash.
I'll get into color temperatures and color balance soon, but this is the most expedient way to make satisfactory portraits.
The point of this strategy is to have enough available light to properly focus. Any more available light starts to create color balance problems unless the available lights are properly color balanced (most aren't).
Alternatively, PJs can arrange the portrait subject, set focus, turn lights off, shoot and then turn lights back on. This is best done with a volunteer near the light switch, but it can be done singly by a PJ in a small room.
Enough for now,