A range of novel and innovative colourimetric optical indicators for commercially important analytes have been developed and characterised. Water-based colourimetric indicator films are shown to have increased operational lifetimes under ambient conditions compared to similar solvent-based counterparts. Response and recovery times, as well as CO2 sensitivity of a water-based, CO2- responsive ink are reported and compared to those of a similar solvent-based indicator. An investigation into the effect of humidity and temperature on CO2 sensitivity was carried out, as well as the effect of plasticiser and base concentration on the response and recovery times. The first example of a colourimetric indicator which detects CO2 levels above ambient pressure is reported. The different sensitivities of the ink over the pressure range 1 - 8 bar are recorded, along with the effect of humidity on the response and recovery of the indicator. Its application as a 'fizziness' indicator is explored and a number of experiments using carbonated drinks demonstrated. The coating of dyes onto inorganic supports, creating a range of intelligent pigments, has opened up a fresh way of developing a new family of intelligent materials. The incorporation of such intelligent pigments into thermoplastic polymers to create a range of flexible plastic indicators is described. The characterisation (e.g. response and recovery times, CO2 sensitivity and effect of humidity and temperature on such sensitivity) of the indicator films revealed similar sensing capabilities as previously reported in the ink films. Two polyoxometalate based indicators are described: an oxygen indicator and a UV dosimeter. The effects on the sensing characteristics of both inks by varying the key components (i.e. glycerol and polyoxometalate) are reported. Illustrations of the oxygen ink being used as a delayed oxygen indicator in food packaging applications are investigated. It is shown that the UV dosimeter can be tuned to match different skin types, by altering the ink formulation.