The old (correct) definition of complementary colors was edited to change it from
the correct RBB
model to the outdated RYB description (that many of us were
taught and school.) The challenge is
updated to use "yellow" instead of "orange".

ISSUES CLOSED: freeCodeCamp#221

Previously I did a PR to fix the definitions of complementary colors to reflect
modern RGB color
theory. This is an adjustment to some of the text, getting rid of "Note:"
and rewording the first
sentence.

ISSUES CLOSED: freeCodeCamp#221