The 1,3-bis(4-aminoaryl)squaraines showed colour change behaviour, they were found to undergo reduction with sodium borohydride in solution to give colourless leuco compounds, which oxidised readily in air back to the coloured squaraine dye. We have investigated this possibility, and have found that reduction can, in most cases, be achieved readily in organic solvents with sodium borohydride, and moreover, the resultant colourless reduced species (leuco dyes) are generally chemically stable and can be oxidised back to the coloured dye with air or common inorganic oxidants. This meant that the 1,3-squaraines could be used as redox indicators, with possible functional applications in enzyme assays, oxygen detection, or reprographic systems, and thus the chemistry of the leuco-1,3-squaraines was investigated in detail in order to determines their potential value in such areas.