Colour mixing is fundamental to learning to paint. Students in visual art classes in secondary schools face problems in manipulating paint and discriminating colour. The kinds of base paints to be presented to students could be an important factor in learning about colour relationships and pigments. The purpose of this study was to determine whether Year 7 students generating colour mixes with paint using a triad of magenta, cyan and yellow were able to mix and discriminate more colours than if they used a triad of red(scarlet red), blue (ultramarine light) and yellow (lemon yellow) which is a base triad commonly used in schools. The Weddell Colour Discrimination Test was developed for use in this study which was a test that involved colour mixing with paint. The study used quasi-experimental designs for both a pilot study and a main study. Results indicated a significant difference in the ability to mix paint advantage of groups that used cyan , magenta and yellow. Implications for the use of particular colour triads in art classrooms and methods of teaching colour theory have emerged from this study. The Weddell Colour Discrimination test instrument developed in this study could be useful as both a diagnostic tool and a teaching tool as well as a data gathering method for further research.