Assert (and if necessary repair) the white/black brightness invariant

A template library learned from a board whose orientation was misjudged has every white template built from a black piece and vice versa. That is catastrophic and silent, so check it explicitly: across the six piece kinds, the white templates must be brighter than the black ones.

Usage

fix_template_colour_swap(lib)

Arguments

lib

A template library from build_from_start_position().

Value

A list with the (possibly colour-corrected) lib and swapped, indicating whether the colours had to be exchanged.