on the color wheel orange violet and green are known as secondary colors
Color wheel The typical artists' paint or pigment color wheel includes the blue, red, and yellow primary colors. The corresponding secondary colors are green, orange, and violet or purple. The tertiary colors are green-yellow, yellow–orange, orange-red, red–violet, violet-blue and blue–green.
Red cabbage The red cabbage (purple-leaved varieties of Brassica oleracea Capitata Group) is a kind of cabbage, also known as purple cabbage, red kraut, or blue kraut after preparation. Its leaves are coloured dark red/purple. However, the plant changes its colour according to the pH value of the soil, due to a pigment belonging to anthocyanins. In acidic soils, the leaves grow more reddish, in neutral soils they will grow more purple, while an alkaline soil will produce rather greenish-yellow coloured cabbages. This explains the fact that the same plant is known by different colours in various regions. Furthermore, the juice of red cabbage can be used as a home-made pH indicator, turning red in acid and green/yellow in basic solutions. It can be found in Northern Europe, throughout the Americas, in China and especially in Africa. On cooking, red cabbage will normally turn blue. To retain the red colour it is necessary to add vinegar or acidic fruit to the pot.