I've noticed that I have 3 different colour variations for my adventure deck with the Main 4ER and 3 expansions so far.
Since I'm not trying to memorize which colour belongs to which expansion, I don't have any idea which card comes with each draw.
If we add, at least 3 more expansions, probably 6, if not more, I would figure you'll have so many different variations, it will be difficult to tell which variation you are looking at when you draw. Besides, every expansion has good and bad cards, so it doesn't really matter if I knew which expansion I was drawing from, does it?
. Variation of colors on the back of any deck of card is bad mostly because you shouldn't be able to tell the cards from the main game from it's expansion. I had high hope with FFG's reputation that this Game Workshop flaw from decades ago would be a thing of the past. And I don't consider a multitude of tones variation from many expansion and the quantity of cards a fix for this
. Basically, tone variation should not be noticable or visible to the naked eyes.