Multicomponent mixtures composed of two group of polar nematics : one taken from tri-ring or four-ring compounds with the cyano terminal group and the second taken from biring cyano compounds were studied. In these systems the induced smectic A(d) phase in the form of a nematic ’island’ surrounded by a nematic ’see’ occurs and after introducing a chiral component a TGB(A) phase is created and a selective reflection of light with a reverse colour sequence upon temperature (from blue to red) is observed. The shape of the induced A(d) phase and the concentration of the chiral components influences the properties of the selective reflection. The mixtures with the selective reflection of light were dispersed in a polymer and the obtained foils were tested as sensors of pressure.