What artistic skill is required to blend colours smoothly in a painting?

Rendering is the artistic skill of smoothly blending colours, tones, and values in a painting or drawing to create realistic transitions and three-dimensional form. It involves carefully working one colour or tone into another so that no harsh boundaries are visible, producing a smooth gradient effect.

Colour blocking is the opposite approach - it places flat, distinct areas of colour side by side without blending them, deliberately maintaining sharp edges between colours. Cross-hatching builds up tone through overlapping sets of parallel lines rather than smooth blending; it creates texture and shading through the density and direction of lines. Pointillism uses small distinct dots of pure colour placed close together; the viewer's eye mixes the colours optically at a distance rather than the artist physically blending them on the surface.

Of the four techniques listed, rendering is the one that specifically requires the skill of smoothly merging colours on the painting surface to achieve seamless transitions.