Guys, thanks for your words much appreciated. By the way, I enjoy the private atmosphere here, as far as it seems we are only three at the GB at the moment.
Dupes, thank you so much for the input very useful to me because it made me think a lot. I think you are right totally and things are not really well expressed by my side and I am sure this all needs better clarifications. Regarding the former step, bear in mind all colurs were airbrushed very thinned, so you are not spraying pure colour in fact and in that meaning nothing is really pure German Grey, pure Earth Brown or pure Buff but clear shades of them. Also the layering -soft edged- effect caused by airbrushing makes everything blend together smoothly naturally (although you can make hard/strong traces intentionally too). At the end, final shade is a product of those two main causes and it is much less traumatic than you might think reading a brief written description.
Waikong, derivating form the above remark, I would recomend you to go slowly with any new thing you want to try until you get the experience to use it with confidence. Do not get me wrong I do not mean you have to pass a long training for that, because particularly this technique permites you to go as far as you want little by little. Next time you want to give it a try, just make the process one single time and stop for a second to see how it goes, if you like how it starts, then add a bit more and stop and see again. I am sure you will reach the point you want easily that way. Anyways, you know what? Even the few times I consider I overdid this effect on any of my models, at the end I realized that I had to have made it a bit more still. Can you believe it?. The weathering is a summ of many things and not the product of one only technique as you well know.
Now, upper hull must be dusted up in order to balance the former effect made on the lower hull and running gear. Diluted enamels work really well for that purpose used in two different ways. First a very selective light pin wash is given around raised details or recesed lines like a traditional dark pin washs. That is particularly useful for riveted or bolted areas, welding seams, etc. Following heavier dust deposits and stronger colour contrast is added in selected places on the model like the angled joins between the plates composing the hull, by dampening the area to treat with clean thinner to put small drops of enamels there and to blend them with a soft brush dampened in clean thinner.
As you can see once more the look of the model changed and it became quite plain indeed. I personally believe exactly this is the point many modeller feel panic when weathering theirs models because it seems you have ruined all your previous work, but the truth is that we must be patient because this is just one more necessary step in the weathering process and things will change drastically again soon.
Have faith.
Lu