In case of additional colors,
the last is used for values equal to the maximum, the first for minima.
If unspecified, these are green and red respectively (I<31 90 32>).
+Multiple intermediate colors will be distributed
+relative to the size of values.
+
+Predefined color schemes are named I<whites> and I<fire>,
+or I<greys> and I<fire256> for 256-color variants.
=item --spark[=<characters>]