Hi Andy,
To be honest about it, I did not intend for the firefly to look like that...it was a good mistake...if want to have the same mistake :-) then here goes....
1) After applying the decals, I sealed it with tamiya TS-13 (gloss).
2) Sprayed Krylon Matt Finish over the whole kit.
3) Washed the whole kit with pastel chalk (white) dilluted in alcohol...to my surprise the kit turned dusty white (but its too white for my taste that it looked like a winter camo). The flat finish might have absorbed the chalk and the alcohol may also have affected the Krylon finish (I think its not that dry yet)
4) In order to rectify the situation, I washed the kit with Tamiya Olive Drab (XF-62). After it dried, I applied the same wash again until some of the whiteness was neutralized -- producing the effect dusty effect.
BTW, the original coat (prior to wash) was a mixture of Tamiya Olive Green (40%) and Olive Drab (60%)...
Hope this helps...and good you liked it...