What can be changed to make a brush stroke light at first and darker later?

Correct answer: Amount of paint on the brush

The governing concept is paint loading and colour intensity. A brush carrying less paint usually produces a lighter or weaker mark, while adding more paint can make the stroke appear darker and fuller. Thus, changing the amount of paint on the brush directly changes the strength of the stroke. The paper’s name, handle colour and table height do not control the applied colour, so option A is correct.