You are both correct.
When mixing light sources directly, R G B are your primary colours from which the impression of any other can be synthesised. This is best described as an "additive" process.
When dealing with natural, reflected light, the colour is actually determined by which parts of the overall spectrum are absorbed by the surface you are looking at. A red surface effectively absorbs all non-red parts of the visible spectrum and reflects only the red. This is best described as a "subtractive" process. It so happens that you can simulate any colour subtractively by mixing red, yellow and blue pigments.
