Why do some people say the Crown and Brow chakras are white and violet while other say violet & blue

There is no correct answer to this question. You can involute into any chakra and get the same color or a different one. It's not the chakra that determines the color, it's more the level of involution. At the end of the day it's a space and when going inward the spaces are many and varied and not determined on which chakra you use.

I've had experiences where I've gone into the Third Eye which is the device I always use and the colors I see range from black, purple, blue, gold, red. I have never had a white space ever in the years of meditation I've done. That does not mean I'm doing anything wrong. It's a furphy to say you are doing something wrong when you get a different color to someone else.

Even though I use the Third eye (which you are calling the brow chakra), it is through this that I can involute into any chakra point. Not all is as it seems in the world of internal consciousness.

I have always been told (because I cannot see auras with the naked eye), that the crown is purple, but the light from it extends, turning into a brilliant white. The brighter the 'crown', the more in tune the person is with the divine. *shrug*