I've been trying to create an interesting one-colored paint scheme with panzer gray.
Something like this:
http://www.steelfury.info/
(By the way, the game will be awsome)
I tried everyhing: preshading with different colors, overspraying, drybrushing... The next will be using a sponge to dab some color on the surface.
Does anybody have any advice on that?
Thanks

You're trying to mimic a 2 dimensional artist's interpretation of dk grey on your 1/35 model surface -- I think you like how it looks but it would be bizarre in 3 dimensional form.

There are many attractive ways to paint 1/35 armor. I don't know if what you see in the painting is reproducable IMHO

It was just an example (I wasn't sure if I can refer to other people's work or not, hence the computer generated image as reference). I don't want to mimic it. I would like to reproduce the effect of irregular gray patches with rust.

I think "mapping" is what you are looking for.

it is fully explained in Mig Jimenez's book (F.A.Q.)

The old fashioned way to create subtle variations in a monotone finish is dry brushing. Not the light dry brushing used to pop out raised details, but a scrubbing action in flat areas using a very subtly different shade of the base color, applied very dry. It's time consuming, and very destructive to brushes, but it can work. Nowadays, most modelers try to get similar effects with preshading or oversprayed glazes (filters, to Mig's fans). However, it's hard to get the chaotic blotchiness that you often see on real weathered objects with an airbrush. Still, it all comes down to a personal artistic choice. Experiment a bit, and see what you like.

You can replicate that effect by applying little dots of White, Blue, Green, Yellow, Raw Umber and Burnt sienna oil colors, in a very random way, over the flat surfaces with a nº0 brush. Then just dip a nº1 or nº2 brush in white spirit, remove the excess with some tissue paper, and start spreading those dots of color, thining them to create "filters" of color over your panzer gray surface.

Thank you all for the answers. I'll try all
(What is mapping? I don't have MIG's book, and will not have it in the foreseeable future...)

Mapping is a fashionable name for that filtering I wrote about. The idea is to create transparent filters over the base coat by applying a pin-head sized spot of paint and then spreading it with a brush with thinner. You can use the same technique to apply a winter white wash, for example, but in that case you could use an acrylic white paint.

Thank you. I didn't know it was called "mapping".
I have limited success with this method: it's pretty good to imitate rainmarks and rust, but I usually end up simply washing down the pigments
I guess it's a matter of practice.

I might be getting it...

What do you think?

Another way of doing this effect is using about 4 variations of the same colour ie lighter shades of panzer grey.
spray one down evenly then spray the next colour down randomly moving the airbrush eraticly aiming to not cover the whole model but only leave random bits of the diffent colour.
Repeat with the lighter tones covering less each time.
The effect should be subtile.
Then Dry brush then add dirt and grime.
Pre shading before you do this could help.
Remember dont start with a darkend shade of the panzer grey start with the original colour then go lighter.

Streaking with oils and chipping with a sponge and some brown paint then adding some metal on highly worn areas can compleate the effect.

Hope this helps.