During reformulation of a liquid laundry detergent, an undesirable color change was observed: the normally blue color of the formulation was found to turn green when exposed to elevated temperatures during accelerated stability testing. Spectroscopic analysis revealed formation of a yellow substance, whose transmission spectrum combined with that of the blue dye to yield the observed green color. Sequential solid phase extraction using cation and anion exchange indicated the yellow substance was a base. Liquid chromatography–mass spectrometry (LC–MS) analysis of the isolate demonstrated a series of related compounds whose elemental composition and fragmentation suggested polyethenyl imines (PEIs). These results support a mechanism involving metal‐catalyzed oxidative degradation of triethanolamine (TEA) with subsequent acetaldehyde‐mediated formation of conjugated PEIs as primary factors responsible for the observed color change.