er</code> (or separate <code>p1</code> and <code>p2</code>). If
<code>power[2]</code> (or <code>p2</code>) for the luminance trajectory is missing, it defaults
to <code>power[1]</code>/<code>p1</code> from the chroma trajectory.
</p>
<p><code>diverging_hcl</code> codes the underlying numeric values by a triangular luminance
sequence with different hues in the left and in the right arm of the palette. Thus,
it can be seen as a combination of two sequential palettes with some restrictions:
(a) a single hue is