Colorimetric detection employs chromogenic substrates, which can be either alcohol insoluble - appropriate for Western blot and IHC, or alcohol soluble dyes, which are suitable for ELISA. The blot is incubated with a chromogenic substrate to yield a colored precipitation. Signal development is arrested by washing off the substrate. Resulting precipitate is visualized directly on a membrane as a band or a dot.

Chromogenic substrates are available for various enzymes: HRP (horse radish peroxidase), ALP (Alkaline phosphatase) , GOD (Glucose oxidase) and β-Gal (β galactosidase).