If a limited poster-colour scheme appears dull, how can variety be increased while preserving unity?

Correct answer: Create tints, shades, and controlled muted forms of the selected colours

Unity comes from retaining a related colour family, while variety can come from changing value, lightness, darkness, and saturation within that family. Tints add white or lightness, shades deepen the colour, and muted versions reduce intensity without breaking the scheme. Thus option B is best. Unrelated colours weaken unity, identical values reduce variety, and only black is too limited.