I worked at an auto parts store which mixed paint, they color matched my stock and I took the paint home in a pint can. They can also charge a spray paint can, too, runs about $30. Fast dry lacquer flat was what we used.
It did match the stock, however, the industry has a hard time matching each other altho there is a specific shade number they attempt to match. The grip is slightly different. The next issue is that as the paint ages, it changes - I top coated with spray Matte Clear which slows abrasion and wear on the high spots, but using the rifle, even carrying it all day, eventually puts on some wear. Some areas picked up soil, others are working down to the original black anodizing - which you do NOT sand off or you wind up with silver highlights. Anodizing is the method the industry uses as primer - storefront manufacturers specify it for their high wear entries.
So the rifle is picking up a mottled look and self camoflaging. Exactly as the krylon jobs in Afghanistan and Iraq did. Battle worn is better. Deer season I'm using ten shot Lancer or Pmags, the 20 and 28 round steel mags I bought will get painted lowers to match as it will ID them as my 6.8 mags.
Just check with an auto paint mixer and supply the piece which most closely matches. Keep in mind FG is weird when rendered by electronic media - background colors in my pics make it change from light bluish green to dark OD. Now add having someone else's color rendering on their display screen - how many different one over the generations? Hundreds - and you get some massive differences trying to match things up online. The electronics screw with it worse than different fabricators.