This paper presents an experimental activity based on the absorption of light colours by pigments. The activity is constructed using a stepwise design and offers an opportunity for students and teachers to compare and generalize the interactions between light and pigment colours. The light colours composing an artificial rainbow produced in the classroom are subtracted using a set-up of refractive solutions containing pigments. Symbolic, diagrammatic and realistic representations are provided to explain and compare the findings from seven steps in the activity.