The RYB delusion
When I learned about colors in primary school, I was taught that the primary colors are red, yellow, and blue. I would bet that you, reader, were also taught in this way. If you do a google image search for 'primary colors', you'll find plenty of images with the specific colors shown above. I am here to argue that we have all been lied to, and that the only correct, canonical, truthful and logical primary colors (for pigments/paint mixing, aka subtractive color) are cyan, yellow, and magenta.
The main failure of the RBY system is that it is impossible to make a decent green with pure blue and yellow. The reason is that pure blue and yellow are actually complimentary colors. If you remember learning about colors from grade school, you'll know that mixing complimentary colors results in brown or grey. Below, I will make your browser generate a gradient starting at yellow and ending in blue.