“By adding two primaries together we end up with the secondary colours: red and blue make purple, blue and yellow make green, yellow and red create orange. The addition of more colours creates tertiary colours, but every time more colours are added, the purity of colour drops until eventually we end up with browns and greys.“David Coles, “Chromatopia”, page 1
I added the bold to the quote. Purity isn’t a word I use when thinking about colour mixing, but it is key.
Keeping the number of pigments in a mixed colour to the minimum. keeps the result further away from an unintentional murky mess. This includes ‘hidden’ pigments in tube colours that are a mixture, such as an orange that is a red and yellow mix rather than a single orange pigment. The name won’t tell you; it’s in the small print on the side of the tube label or a manufacturer’s colour chart (and on the product info of some art materials shop websites).
For instance, looking at Golden Heavy Body Acrylics, the Cobalt Teal might be the colour you’re after but when you look at the price you realise it’s a Series 7 colour, gulp, so you might decide to go with the Teal instead or perhaps the Light Turquoise (Phthalo), because they’re fairly close in colour . But whereas Cobalt Teal contains contains only PG50 (a green pigment), these contain PW6, PB15:4, PG7 (white, blue and green) and PB15:4, PW6, PG7 respectively (blue, white, green).
Mixed tube colours aren’t inferior, they’re just mixtures. This becomes relevant when you’re then mixing colours using these as you’re mixing with mixtures and so have more ingredients (pigments) than you might realise. Knowing what’s in the tube when you’re colour mixing is one of the keys to not inadvertently end up at greys and browns.