hi
i was wondering how do u fade decals when it comes to weathering

Fading away can be done by airbrushing (the whole model usualy) by buff colour to pretend dust and sunfade in generall and also using fine pastels powders , and being patient cause the glossy surface of the decals won't keep the pastels on easily till you nrush on a flat varnish. Furthermore you can use very uch dilluted dust like colours to pass over decals but take care of what thinner u use or you can dillute the decals instead !!!!!!

See Mal's (aka Holdfast) article on his Corsair for a beautiful example of decal weathering. https://armorama.kitmaker.net//features/249&page=4 That guy is the master.