A "power tie" is one that is of such striking color
that it attracts the eye and makes the wearer stand out from those around him (or her). Usually red or yellow, the power tie is a legacy
of the 80's and Ronald Reagan's
The story is that he was the initiator of the wearing of these bold ties, but the credit is believed to actually go to a newscaster in the White House press pool.
According to the story, the reporter was tired of never getting called on so started wearing bold red ties to the press conferences to get Reagan's attention. Not only did the reporter get noticed by the President at press events, Reagan adopted the bold style to the point where the first use of a "power tie" is attributed to him.
shaogo points out that Brooks Brothers had a line of bold ties prior to Reagan's popularization of same and CEOs and their ilk would often in the past use such a tie for their impact. However, Reagan took the concept and made it a household name.
rootbeer277 reminds me to point out that it isn't just a loud or garish tie, it is one that is bold and "forceful". A fish tie or one featuring the first issue of spiderman may be impressive to some, but is not a power tie.