Three color interpolation scales demonstrate how D3.js v4 maps numeric domains to color ramps, rendered as rows of circles in SVG. The first scale interpolates from red to green using two stops, the second adds a middle yellow stop, and the third uses eight discrete stops for a finer gradient. Each scale employs `d3.scaleLinear` with the `d3.interpolateHcl` color interpolator, while the circles are generated programmatically from a simple data array. The example illustrates how interpolation choice and stop density affect perceived color transitions.