Why may two dry acrylic samples of the same mixture appear different?

Correct answer: Layer thickness, surface texture or surrounding colours differed

The governing concept is colour perception in context. Although the wet mixture may be identical, a thicker or thinner layer can change its apparent value and opacity; surface texture changes reflected light; and neighbouring colours can create contrast effects. Thus option B is correct. A brush name or colour name does not alter the dried paint by itself, and coloured water is not the general explanation.