l_hcl</code> for sequential palettes with a single or
multiple hues, and <code>diverging_hcl</code> for diverging palettes (composed
from two single-hue sequential palettes).
</p>
<p>Two different GUIs are implemented and can be selected using the function
input argument <code>gui</code> (<code>"tcltk"</code> or <code>"shiny"</code>). Both GUIs
allows for interactive modification of the arguments of the respective
palette-generating functions, i.e., starting/ending hue (wavelength, type of
color), minimal/m