I will normally get a grey wash that can be seen in the bore of my wheel guns. It dont worry me because it remains just a grey wash for the duration of how many ever I fire between cleans.

The levergun however is a different critter, very hard to detect by eye from lube and powder fouling.
If it is leading from a particular load, first coulpe of patches during clean up tell me.
Flakes or even streaks of lead will be present on the patches.