Imgur link is from Barbara Brennan's Core Light Healing (Chapter 6). tl/dr if you shift your energy column forward and activate the front of your third eye for viewing you get colors but if the back isn't active you don't get form. And vice versa you will get form but no colors if the back is working but your energy column isn't balanced to run the front part.
I've also noticed when I shift into analysis mode my awareness tends to move forward and away from the center column pulling me away from the target and into my own thoughts. This also implies that if you have trouble seeing certain colors or getting color in your vision at all, the front needs work, and likewise for working on forms in the back. The rest of the chapter is pretty good and talks about tuning into different layers of energy fields.
VPC is Vertical Power Current, another name for the column of energy that runs along the centerline of your body