What change occurs when the amount of red is increased in violet made from blue and red pigments?

Correct answer: It becomes red-violet

The governing concept is colour bias in subtractive pigment mixing. Violet is produced from blue and red, and increasing the red proportion shifts the mixture toward the red side of the hue range. Therefore it becomes red-violet. Increasing blue would instead produce blue-violet; green requires a yellow component with blue, and neutral grey would require balanced neutralising mixtures rather than simply more red.