Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability, to provide dedicated surface functionality, and for size and shape control. The resulting micro-nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution-processing of (opto)electronic devices. As examples phthalocyanine nanowire transistors, as well as quinacridone nanocrystal photodetectors with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly-attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally-friendly alternative to inorganic nanocrystals, as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants.