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.
Methyl orange In an acid, it is reddish and in alkali, it is yellow. Methyl orange has a pKa of 3.47 in water at 25 °C (77 °F).[2]