'Hidden' catalysis limits not only catalyst and reaction development, but also mechanistic understanding and application to large scale settings. The state-of-the-art methods to identify 'hidden' from 'true' catalysis requires extensive effort and kinetic analysis, thus routine adoption has yet to be realised. Catalysed hydroboration reactions are no exception to this and are plagued by hidden borane catalysis. The majority of new catalytic hydroboration systems contain nucleophilic motifs which are capable of decomposing HBpin and HBcat, generating catalytically active BH3. Crystal violet, (tris(4-(dimethylamino)phenyl)methylium chloride), a benchstable and commercially available reagent, was used as a colourimetric indicator for 'hidden' borane catalysis for species from across the periodic table. A colour change from purple to colourless indicated the presence of BH3, and thus the potential for 'hidden' catalysis. The crystal violet indicator was successful at determining BH3 generated from the nucleophilic-and 'catalyst'-mediated decomposition of HBpin. Crystal violet was found to not inhibit catalysis, or react directly with substrate, HBpin and HBcat, nucleophilic species and the 'catalysts'