depends- if you mask things you dont need to take anything apart. Myself these days I take the gun apart and just paint what I need.
Krylon likely has a decent grey (they have a camo line but I dont recall if they have a grey in that line). Watch out though as multiple layers of spray paint on Krylon tends to produce a 'crackle effect' into the paint giving it a texture.
I have plenty of clear guns and JG guns to compare: in terms of plastic my clear G3/R72 holds up just as well as my nonclear JG ones and the non-clear PulseR72s.