Self-assessing polymer blends based on poly(ethylene terepthalate glycol) or linear low-density polyethylene and small amounts (0.5-2% w/w) of chromogenic sensor dyes are prepared and investigated. The cyan-substituted oligo(p-phenylene vinylene) dyes employed in the study exhibit pronounced optical absorption changes upon self-assembly, because of charge-transfer interactions or conformation changes. The extent of dye aggregation (and therewith the optical absorption characteristics) in these blends is significantly influenced by exposure to external stimuli. Subjecting appropriately processed samples to either temperatures above their glass transition or mechanical deformation can significantly change the extent of aggregation, which in turn leads to a color change.