Pararosaniline is used as a colorimetric test for aldehydes, in the Schiff test.
Alcians blue carries Phthalocyanine one of the most highly colored chromophores yet known with a molar extinction of 120,000 i.e. AB is detectable at half the molar concentration of popular dyes like toluidine blue, tryarylmethanes (e.g. pararosaniline and the analogous Schiff bases used in PAS stain, Crystal violet in Gram stain) etc.