An amine-reactive blue fluorescent probe that provides a distinguishable contrast when used with longer-wavelength probes in certain multicolor fluorescence applications such as nucleic acid and protein microarrays, in situ hybridization and immunofluorescence. This carboxylic acid derivative of 7-methoxycoumarin can be used for coupling to amines, hydrazines or hydroxylamines on biomolecules of interest. Spectral data: Ex=336nm, Em=402nm (Buffer, pH9).