Gee Dennis, I appreciate the call-out but I am simply standing on the shoulders of those who came before me and shared their knowledge. Add to that a rather large pile of ruined leather that I've attempted and failed. It is certainly part of the learning process for me. I just threw away a knife sheath this weekend that came out......well.....not good.
Controlling the finish has been my goal since my first bag. A huge vote of thanks to James Rogers of course for his coaching along the way, and responding to my repeated cries of distress. I dye and finish everything possible before assembly, and then touch things up afterwards. It is much easier to get a nice, smooth even finish if it is laying flat. You don't have to fight to get dye into the cracks either. If I ruin one panel, I haven't wasted time and ruined a whole project. And I've ruined a ton of panels.
I love the color of the body of your bag. That looks rich and warm. If it were me and that flap came out that dark, I'd go one of two ways. 1 - Cut off the flap but leave enough for a hinge at the top, and sewn on a new flap. 2 - Use Neatsfoot oil and Fiebing's antique glaze to try to creep the body of the bag closer to the flap color.
In my experience, leather is like a pair of Pampers or a one-way sponge. The unfinished/back/suede side will suck up any liquid you put on it, and deliver it in minutes to the finished side. Conversely, you can slather stuff on the finished side and rarely see any evidence on the unfinished side. Yep, I did this wrong in the past and ruined some leather. See a recurring theme in here? ;-)
I dye the backside of leather just enough to get some color and life into the look, using thinned Pro-Dye on a piece of sheepskin and scrubbed in. I mistakenly tried oiling the unfinished side in the past, and suffice it to say that it did not come out well. The oil goes on the finished side. I was told by one very experienced leatherworker that you put Neatsfoot on a papertowel, and rub in a thin coat. If it soaks in before 2-3 seconds, you can add another coat. If it soaks in slower than that, you have fed the leather enough.
I have not had any luck with the Eco-Flo dyes, but you seem to have gotten a nice color.
Difficulty finishing the back, rough side of leather is why I line things now whenever possible. Since you were already edging your flap, it would have been simple to line it first, and avoid dye work under the flap.
Your construction work on the bag looks really nice.
I hope this helps a little. Feel free to give me a call. God Bless, Marc