d3.interpolateCubehelix()

d3.interpolateCubehelix(a, b)

Or, with a gamma of 3.0 to emphasize high-intensity values:

Returns a Cubehelix color space interpolator between the two colors a and b using a configurable gamma. If the gamma is not specified, it defaults to 1.0. The colors a and b need not be in Cubehelix; they will be converted to Cubehelix using d3.cubehelix. If either color’s hue or saturation is NaN, the opposing color’s channel value is used. The shortest path between hues is used. The return value of the interpolator is an RGB string.