How should a hard band between colours be corrected while creating a gradation with poster colour?

Correct answer: Prepare an intermediate mixture and apply a controlled layer over the dry band

The governing blending principle is to reduce a sharp value or hue change through an intermediate transition colour. Mix a colour between the two existing colours, allow the problematic band to dry, and apply a thin controlled layer so the boundary becomes gradual. Thus, option A is correct. Black changes the design, hard rubbing damages the surface, and excessive water can cause streaks, puddling, or paper damage.