Aims: Whitening has recently been one of the most demanded treatments in modern dentistry practice. The authors tested three hypotheses related to color changes on universal nanofilled composite resin samples promoted by in vitro tooth brushing with the usage of different whitening toothpastes. Methods: For this in vitro study, a total of 8 different whitening toothpaste test groups and a control group, where each test group included 10 randomly selected composite resin samples, were formed. After all composite samples were light cured and polished, they were stored in distilled water, kept immersed in red wine and subjected to brushing, consecutively. Colors of the composite samples were measured by using a colorimeter device after each process. Results: For all test groups, we observed that the discolorations on the samples due to immersion in red wine were reduced significantly after brushing with or without a toothpaste. Color improvement promoted by one whitening toothpaste brand containing hydrogen peroxide as bleaching agent was significantly higher than in the control group. Statistically similar color improvement values were observed among whitening toothpaste test groups, when compared to each other. Conclusions: From the results of our study, it can be concluded that: Firstly, only one of the whitening toothpastes showed statistically significant color improvement over the control group; secondly, the color improvements promoted by whitening toothpastes, used in this study, were statistically similar.