That's too bad that you couldn't find a 3D bag that you loved. In general I've found that sometimes you need to shop around with Longchamp bags, because the leather quality, color, workmanship/stitching or even the dimensions or strap lengths can vary slightly for bags of the same of model. I suspect this has something to do with the country of origin, or the individual factories, where the bags are manufactured. For instance I own two Roseau Croco totes from fall 2016, one made in France, one made in Tunisia. The bag made in France has much nicer leather, and the length of the toggle closure loop differs dramatically on the two. I'm not saying that all made in France bags are superior, because I have some very nice quality Longchamp bags made in other countries, including China. But there can be noticeable differences based on where a bag is made.
I also know what you mean about varying color saturation on the 3D line. Longchamp says the line is made of "washed matte calfskin" and I've seen some 3D bags that look a little splotchy or lighter than I would care for. When I was shopping around for the 3D line the past couple of weeks, I can remember trying on two of the hobo/crossbody style bag in the Blue Mist color (at
Nordstrom and Bloomingdales) and the blue color was nice and even, actually more even than on the Cognac. I bought my Cognac small tote at a Longchamp boutique and the color is even and the bag is pretty structured and stands up on its own.
So perhaps you could roll the dice and order a Blue Mist 3D tote from longchamp.com or a department store website and you would be happy with the results. Its hard to say. I don't mean to send you on a wild goose chase but I just thought I'd share what I know. Good luck.