Which process is correct for creating a gradual strip from light to dark values of the same colour?

Correct answer: Gradually vary the amounts of white and black

The governing concept is a value scale, a controlled progression from light to dark. Increasing white creates lighter tints, while increasing black creates darker shades; varying these amounts gradually produces related steps of value in the same colour family. Therefore C is correct. Different primary colours change hue, equal water does not create a full value progression, and excessive complementary colour can neutralise the colour rather than form a clean scale.