Purpose: This study evaluated the colour changes of demineralized enamel after treatment with coloured fluoride gel. Materials and Methods: Enamel blocks obtained from bovine incisors were submitted to artificial caries induction by pH cycling followed by fluoride gel applications (2% sodium fluoride, pH 6.8) using a colourless gel (control group), pink or blue gels. The enamel optical properties were evaluated by spectrophotometry, using the CIE L*a*b* system at baseline (sound enamel), after artificial caries induction (demineralised enamel) and after each of the five fluoride gel applications (weekly intervals). Changes in enamel optical properties (ΔE) were analysed by two-way ANOVA and Tukey's test (α = 0.05). Results: No significant differences were found among fluoride gels (p = 0.476) regardless of the presence of pigments in the gel. ΔE values were significantly different (p 0.001) between baseline evaluation and treated enamel (after fluoride gel application). Conclusion: This in vitro study demonstrated that colour changes in enamel do not occur during fluoride gel treatment, regardless of the presence or absence of coloured pigments in the gel. Keywords: bovine teeth, demineralization, dental enamel, fluoride, spectrophotometry