Well folks,
I think I landed on a surefire method to duplicate this kind of result. Funny I didn't think about the solution more quickly since I have used something similar in my old miniature painting days.
I will use very thin washes to get that result. That will assure I get dye where I want it. I can also achieve very gradual fading. To show you what I mean, go to the link below. The technique is very well demonstrated by Hongbo Zhang, a Chinese artist that works on leather. Probably not something that will be easy to master but I think the results will be very fine indeed.