Successful use of numbers is important in almost all areas of modern life. Research on numerical cognition indicates that the mental representation of numbers has its foundations in sensorimotor experience and that the representation of numerical information is also linked to other quantitative dimensions, such as brightness. A theory of shared magnitude and the mental number line hypothesis have provided spatial explanations for the relationship between numbers and brightness. However, there are other possible explanations that explain the interaction through indirect or non-spatial mechanisms, such as theory of metaphorical mapping and the polarity correspondence principle. Thus, the aim of this research was to examine whether there is an interaction between brightness, colour, and arithmetic operations of addition and subtraction. The study involved 60 participants which were divided into two groups. The first group of participants (n=30) took part in an experiment that examined the interaction between brightness and arithmetic operations, while the second group of participants (n=30) took part in an experiment that examined the interaction between colour and arithmetic operations. The results showed that participants were faster in verifying addition tasks when presented in white font compared to black font, and in verifying subtraction tasks when presented in black font compared to white. In the second experiment, no significant interaction was found in terms of reaction time, but it was observed in terms of efficiency and accuracy. Furthermore, the results indicated that the relationship between brightness, colour, and arithmetic operations is more complex than expected, and a three-way interaction was found between brightness or colour, arithmetic operations, and response.