Which tertiary colour is useful for creating a deep pink-like effect in flowers?

Correct answer: Red-violet

The governing concept is selecting a colour by visual resemblance and colour mixing. Red-violet lies between red and violet on the colour wheel and can produce a rich pink, magenta, or deep rosy effect when used in flowers. Blue-green suggests cool foliage or water, yellow-green suggests fresh leaves, and yellow-orange creates a warm golden effect rather than a deep pink one. Therefore, option A is the correct choice.