Everyone knows that blue and yellow make green and red and yellow make orange. But the colours on your monitor use RGB (Red, Green and Blue) pixels. The three colour pixels together make white. The three colours of paint together should make black but they actually make a muddy brownish/greyish colour. The problem here is that paint is a subtractive medium and light is an additive colour medium. By subtractive I mean that paint absorbs all colour except the colour that we see. And paint is a very inefficient colour medium. That’s why four inks are used in printing; Cyan, Magenta, Yellow and Black. Cyan is sort of blue. Magenta is sort of red. Yellow is Yellow, although somewhat on the green side, but ink is more transparent. Black is exactly that but you can’t make black with the other three colours in a subtractive medium.
Most colours used in printing use four colours. Yellow, Magenta and Cyan set the colour and black is added to set the tone. White is just the plain paper without ink. I use paint in a similar way. I try to stick to only two paints to set colour and black to darken. I use white sparingly. If I’m trying to match an intense saturated colour I almost always resort to a particular paint or pigment. Specific pigments or paints that I use most often are Quinacridone Crimson, Dioxazine Purple and Naphthol Crimson. The pigments used in these are relatively new; early 20th century. Oil paint tends to use traditional pigments and most of the overly poisonous ones have been discontinued but there are quite a few poisonous pigments. Artists were more concerned with the colour than poisoning themselves.
So I decide what two paints I’m going to try then add white or black. Hopefully that method comes out OK. Hansa Yellow is very transparent so I add it whenever I want the colour to be warmer. So far Ultramarine Blue is the only colour that I haven’t found a modern pigment that I like better. Originally Ultramarine blue used Lapis Lazuli for the pigment; not poisonous but expensive. It now uses a somewhat modern and far less expensive substitute so perhaps I don’t need to look any further.
There is no shortage of opinions on colour. I use the web and see if anyone has a better solution for a problem I might be having.