Expanding the Range of Primary Colors
Every color brings a chromatic richness to the other primary colors in the same shade. Because each primary color includes complementary hues, the chromatic range of reds, blues, and yellows is broadly covered.
Prussian blue (PB27) gives an interesting depth to ultramarine blue (PB29). As for phtalo blue (PB15:3), when combined with ultramarine blue it creates a magnificent, deep, luminous ultramarine.
Cerulean blue (PB36) and ultramarine blue combine to create a blue that is very close to true cobalt blue.
The addition of a hint of phtalo blue or Prussian blue to cerulean blue creates shades of turquoise cerulean blue, which are similar to those offered in the color charts of some color manufacturers. ...