Hi Pablo,
im not an expert by any stretch of the imagination however ive learned from these guys here a formula ive had great sucsses with. i use tamyia XF-62
OD green lightend with either XF-57 Buff or XF-55 Deck Tan as basecoat.
i then lighten the basecoat even more and spray most of the flat panels and
in between detailed areas leaveing the darker basecolor showing. if you want a more dusty look before decals and washes you can lighten the mix even more and ad thinner so it is kind of watery but not too much. then give the whole model a very light dusting. you can also use XF-60 Dark Yellow to lighten insted of XF-62 & XF-55 for a different tone. you might want to test the mixes on something first to see what you prefer. i hope that helps a little pablo.
i dont really know the mix ratios as i just do it by feel so to speak.
Good luck with your project.
Cheers!
Gary