There are already questions on disabling flyspell (see: https://stackoverflow.com/questions/3423638)
However I would like to toggle flyspell at runtime.
An annoyance I've found is the red-underline persists, even once flyspell has been disabled.
Closing and opening the file refreshes, but that's impractical.
eg:
(turn-off-flyspell)
(flyspell-mode 0)
;; force refresh of highlighting (doesn't work)
(font-lock-fontify-buffer)
Is there a way to clear underlined text?