What is the best way to check the quality of colour filling?

Correct answer: Check evenness, boundaries, and unfilled gaps

The governing quality criteria for colour filling are even coverage, controlled boundaries, and complete coverage without accidental gaps. The artist should inspect the painted area under normal viewing light and check whether the colour is distributed consistently, the edges remain within the intended outline, and no paper shows through unintentionally. Thus option A is correct. A colour name, brush price, or the back of the paper cannot adequately judge the finished application.