What is the most suitable basis for checking the quality of colour filling and blending?

Correct answer: Even coverage, clean edges and smooth transitions

The governing concept is evaluating the visible result rather than the cost or label of materials. High-quality colour filling should cover the area evenly, keep boundaries clean and create smooth transitions where colours meet. These criteria assess both control and finish. Paint price, brush size and the title may be relevant to other decisions, but none alone proves technical quality. Thus, option B provides the most complete and suitable basis for checking the work.