IMO, when it comes to grill Silver Argent being light or dark? The correct answer is "none of the above".
The reason is that while most will say that Light Argent is correct (and I would agree) the actual shade varied somewhat during production according to original examples I've seen. Some were slightly darker than others but none were even nearly as dark as the "Dark Argent" you typically see on items such as 71 Rallye Wheel Center Caps, etc.
What complicates and confuses this subject is that many dealers sell what they often call "Correct" Light and Dark Argent paint that is not even close to the original shade. If you want truely correct you'll need to have someone like Mike at AllTrim Specialties paint your grill, he's one of only a couple sources I would even consider if perfection is the goal.
The other thing that complicates things is that old Silver Argent paint fades, oxidizes, and sometimes darkens with UV exposure (like 30 years of sunlight will typically do to any paint, especially silvers) so matching an old painted part that's seen even moderate sun exposure is not a good sample to match to when comparing paint. The other curve ball is todays metallic flake paint additives which are a different material than originally used in the Argent formulations, it's nearly impossible to match exactly unless you have some NOS componants to mix your new paint with.
