Abstract Solvatochromic dyes that exhibit a negative or a positive behaviour may be distinguished and their solvatochromism predicted with the aid of DFT-based indices, such as their electrophilicity ω , hardness η and by the Fukui electrophilic functions f G + of the donor and acceptor moieties of the molecule, calculated in the gas-phase and in solvents treated as polarised continua. The protocol was successfully applied to 10 examples of phenolate betaines from the literature, five of them exhibiting a negative and five a positive solvatochromism.