This paper presents the results obtained after experiments concerning on the influence of thermal treatment on color of carrageenan gels colored with carminic acid and colorant Ponceau 4R. Model systems analyzed were maintained on the thermostat for 15 minutes, respectively, 30 minutes, at a temperature of 400C, 550C and 700C. Transmittance of samples was measured before and after the heat treatment, with the spectrophotometer Spekol provided with re-emission accessory R 45/0. Was obtained a decrease of lightness of the carrageenan gels maintain in the thermostat at 400C and 550C, and an increase of lightness gels maintain in the thermostat at 700C