Rewatching The Walking Dead, I noticed a scene where Daryl goes through Merles drugs and in the bag was Walt aka Heisenberg's blue meth.
From my quick google research, pure meth is never blue an inconsistency in Breaking Bad which means any meth should be shown as its normal colour outside of the Breaking Bad universe.
Out of universe, this is explained that since both shows probably use the same props on the AMC network, however I'm looking for in universe or director/producer comments that give some indication that they could be in the same universe.