I think he means you can see the metal brighten up because it is having lube removed from it. I've noticed this on my Beretta Cougar, which is the only gun I use Gun Scrubber/Brake Cleaner on.
I tend not to use the spray stuff on my long guns, mostly because they don't have a lot of hidden internals (especially the pump gun, talk about simple). But the Beretta has all manner of nooks and crannies that you just can't get to with a brush or q-tip, like iniside the firing pin area and such. I use the spray to clean out these enclosed areas, and then apply some generous lube after its dry. And I only do that once every 1000 rounds or so.
I find that my new (and only) AR is not difficult to clean without using the spray, I use Hoppes to clean the bore and bolt carrier group, etc. and then lube with CLP.
~AbM