I was told by someone at a local B&M vape shop that the reason I don't get much flavor, if any, from VG juices is that VG is just not able to bind with and hold onto the flavoring used in it, and that PG is necessary for the flavor to come through or last any length of time at all in the juice. This would seem to make sense and corroborate my experience with 100% VG juices as those I have bought have proven harsh and tasteless.
These juices were also 18mg nic juices, which I was told accounts for the harshness of them, and also for them turning dark because of heat over time, that being attributed to the action of the nicotine in them when heated.
So, is any of this true?
Not true as far as 100% VG juice having little to zero flavor, blatantly untrue. I am not a juice expert, and I don't DIY, however I have vaped a large volume of 100% (or as close as I can get depending on vendor) VG liquid over the past 18 months. I have had many different 100% VG juices from numerous vendors that have been rich and full of flavor...
Tennessee Cured, Ranier and Island from Johnson Creek
Caramel Creme from Virgin Vapor
Gorilla Juice, Bobas Bounty, Havana Gold and many others from Alien Visions E-Juice
Legend, Heavenly Army and Mocha Java Smooth, among others from Heathers Heavenly Vapes
...I could go on with this list but I think you get the point. My all time favorite juice is Hype (peach flavored) from Alien Vision E-juice, it is great, full of flavor, though it is 90/10 VG to PG. If I remember correctly the top juices in the annual ECF poll were all VG juices. If you are having a problem with VG juices I would recommend trying different vendors and/or different juices.
To the best of my knowledge, again not a juice expert, the change in color of liquid is not related to the nic in the juice, but rather the result of exposure of the juice to sunlight and heat, and the buildup of gunk on the atty/carto coils leaching back into the juice. I see no noticeable difference vaping Hype at 18 mg versus Hype at 6 mg as regards the change in color of the juice.