Which method is correct for creating several darker versions of the same colour?

Correct answer: Gradually add small amounts of black paint

The governing concept is shade formation through controlled value change. Adding small amounts of black to a base colour lowers its lightness and produces progressively darker shades. Thus, option B is correct. White would create lighter tints, not darker versions. Increasing water usually changes transparency, flow, or paint consistency rather than reliably making a darker shade. Yellow may alter the hue toward a warmer colour but does not provide a general method for darkening every base colour. Black must be added cautiously because it can overpower the original hue.