I don't trust jack except for my experience. But something to focus the imagination on is helpful.
Same here. Striving for 'The path of the master'.

Also, what happens if someone is blind? The colours would of no use to them.
They only exist as colour when we choose to see them that way, in view, they are just energy centres. I don't trust most literature on this topic, but I do trust my own experiences.
Yes, good point and the same as what Tom Campbell think about it all when interviewed by Robert Bruce. Although applying color to them helps me target and individualize the chakras I believe it is unnecessary, and you can just 'feel' them without adding color to them.