TRIP (Transformation Induced Plasticity) steels, also referred to as TRIP-Assisted Steels, constitute a class of advanced high-strength steels characterized by their complex multiphase microstructures. These steels are extensively employed in the automotive industry due to their superior combination of high tensile strength, excellent ductility, and relatively low weight, which contribute significantly to vehicle lightweighting. Typically, these alloys present low carbon content, combined with small additions of alloying elements such as silicon, manganese, and aluminum, which play a fundamental role in suppressing carbide precipitation and stabilizing the retained austenite phase. From a metallographic perspective, one of the major challenges lies in the accurate identification and quantification of the individual phases present in TRIP steels. Conventional chemical etchants are usually insufficient, as they fail to distinctly reveal the multiple phases associated with such complex microstructures. In this context, this work reports the application of the LePera reagent to distinguish the multiphase constituents. The etchant was prepared and applied following standard metallographic procedures to ensure reproducibility and reliability of the microstructural characterization. The application of the LePera etchant produced a distinct contrast between the phases present in the TRIP steel microstructure. Ferrite grains were revealed in shades of blue, while bainitic regions appeared in a characteristic brown coloration. The martensite–retained austenite constituent (M–A), which cannot be distinguished into its individual components through this reagent, was observed as bright white areas distributed within the matrix. Although LePera etching provides valuable insight into the distribution and morphology of these phases, it does not permit the separation of martensite and retained austenite, which remain indistinguishable within the M–A constituent. Therefore, complementary characterization techniques or alternative chemical etching methods are necessary to achieve a more precise differentiation and quantification of these critical microstructural constituents.