The chromatic transition from blue to red phase of PDA is caused by the electronic structure of PDAs' backbone which is featured by the alternative carbon double bond and carbon triple bond. Upon exposure to the external stimuli such as thermal, chemical and mechanical stimulus, the conjugation effect will endow the chromatic properties to this type material. As far as the pure or "intrinsic" PDAs are concerned, the blue to red phase transition is irreversible, however if the head groups of the PDAs' side chain are strengthened by other structure, for example chelation with metal oxide nanoparticles, it could provide resilience of the backbone to conduct the reversible color change. Several recent researches which assisted by DFT simulation have shown that the chromatic properties could be modified by adjusting the side chain structures of PDA. With the development thin film fabrication technology such as inkjet printing, PDAs could be coated on different substrate materials as multifunctional sensor, for example Kapton films, aluminum foil or even conventional paper.