Are you trying to use a soft edge or hard edge camo scheme?  I've found doing a camo scheme soft edge toned downt he contrast a bit.  Also, you can lighten the colors for scale effect.  Other's with more experience will chime in I'm sure.

I use silly putty to mark my color demarcation lines. Don't paint down into the edge, but rather straight on to the surface. This causes the paint to feather down from where you are spraying and into the edge of the putty, which is not in line with the airbrush. In a sense you are over spraying the demarcation to give it a soft edge you see on the real planes.

BK

If doing a filter you'll want it very thin, almost like tinted thinner. Probably something like a light tan on a green/brown plane or light grey on a grey plane. Build it up slowly with multiple light passes until it gets almost where it looks perfect and then stop and let the thing dry and look over her for a day or two. You don't want to go too far since you can't take it back once done- but you can always add an extra layer or three if you don't think you added enough.  

Ok, on the previous Flanker the shades might have been too dark to begin with and I think I might have used straight masking tape.  I have silly putty and planned on a softer edge camo scheme.   Maybe these will help?

Thanks for the replies,

Dave

Thank you Gamera!  I think I got the jist of it.  I think I'll airbrush with lightened tones and silly putty and if that still doesn't do it will try a blue/gray filter.

Thanks

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Look for tips and videos. Then it's just trial and error till you find a method that suits your style. Good luck with it.

BK