This is just an observation-- I put new tires on in January and have been using DG tire and rubber dressing once a month, always after a wash. I always use a brush on the tires when washing and have never noticed anything unusual, but I haven't really been paying attention either.
I've been wondering about this "out gassing" since I bought the tires. So last night I noticed a spot on one of the tires and went with a paper towel to just wipe the spot off--- and the towel was JET BLACK. So I went around and did the rest of the tires. With just the slightest pressure, every pass was jet black. I mean it was seriously like wiping up a mix of charcoal and India ink. And it just kept coming and coming. Probably a mixture of tire dressing and road grime. If you see a brown film while washing it's called blooming.
I'm not concerned or anything. Tires look totally normal. Just an observation- and proof that SOMETHING is still coming out of the tires (Michelins) after 5 months. As easy as it comes off, the DG certainly isn't "locking" it in. I don't think. Anyway, just thought I'd share.