What should be used to lighten violet without deliberately greying it?

Correct answer: White

The governing concept is the distinction between a tint and a neutralised colour. Adding white increases violet’s value and creates a lighter tint while largely preserving its violet hue. Therefore, option A is correct. Yellow, green and orange are related to violet through colour contrast or complementarity and would reduce its chromatic purity, causing it to become duller or greyer rather than simply lighter.