what is the next step?

Use the airbrush to "dust" the basecoat and apply accent to panel lines etc. You may use pastels to acheive these effects or coat with future and apply washes. I used both pre and post shading on the hellcat below to acheive that "broke in" look.

An alternative or augmentation to airbrushing is washes and pastels. The 1/72 Spitfire below was given a lightly applied dark wash, mostly streaking back along the direction of airflow. If you want the heavily emphasize the panel lines, something that looks unrealistic to me but is popular these days, you can flow more wash into them to make them more pronounced. I think understatement here is better than overstatement. On the green areas, I applied artist's pastel chalk, a light brown color as I recall, kind of grinding it in with a Q-tip. I also used some dark chalk to give some subtle streaking behind the guns as well as make the exhaust stains off the manifolds.

I don't know if the pilot's boots usually wore away the paint below the cockpit on ME-109's. I simulated the typical Spitfire wear by dry-brushing some silver on the wing root. After a final flat coat, everything looks pretty good. The main idea is to kind of tone down the contrasts, put in a little uneveness and color variation, and add a little dirt and weathering. Again, I think understatement is better than overstatement. If for no other reason than the fact that you can always add more weathering, but if you over do it, it can be a real bear to undo an overdone effect. Go slow and be creative!

Curt - I know exactly what you are talking about... I recently did a N. Africa Martlet Mk.IV and it looked like a neon sign! (middlestone uppers and light grey lowers.. similar colors to the desert orange/light blue you are talking about)

What I did on the uppers is use a VERY thin coat of the main color (as in around 85% thinner or so, the rest paint... and I lightly misted it from about 8 inches or so at a med pressure. I did this on the sides too as this helped blend the demarcation line of the upper and lower colors... I didn't do it on the bottom.

THEN - as crockett and andy said, I used pastel chalk, in this case a kind of ochre color with a bit of brown chalk mixed in (trying to simulate the sand in N Africa which is a yellowish to brown color) I dusted over the whole model including the bottom. Once sealed with sealer it didn't show all over the model but tended to show on the higher panel lines where the dust would collect... after the future cured I did a little washing here and there to simulate oil stains and accent the panel lines.

Finally for the chalks, most art stores carry packs of "earth tone" pastel chalks... just grind the right colors up (in this case the dull yellow and reddish brown ones, less of the brown) and with a wide soft brush brush them over the model and panel lines, more emphasis on the leading edges of the wing and cowl...

Good luck to you!! You're right, it kind of looks like a toy when it such contrasting colors with no wear... Oh and I agree with Andy, an understatement is much better than overstating the wear... go little by little till it looks right to you...