Change Invistext (color=transparent, usually used for spoilers) to blurred text, hover for less blur, hold down mouse button to reveal hidden text.

blurtext-spoilers.css

/* Invisitext to Blurtext

Author:  Erik Youngren <[email protected]>
Webpage: https://gist.github.com/Artanis/d7bc3266f3b8c383bf11
Licence: http://opensource.org/licenses/MIT
Targets: http://forums.sufficientvelocity.com
         http://forums.spacebattles.com

README
======
Text in forums that is hidden using the [color=transparent] tag is
very difficult to notice, being invisible and all.

With clever use of the CSS, the markup for this tag is hunted down and
forcibly re-styled.

- Invisible text becomes blurred. The text remains unreadable,
  preserving the intent to obscure the text.
- Hover over blurred text and it becomes less blurred. This is not
  useful, but it sure looks neat!
- Hold down mouse over invisible text to clear the blur and un-hide
  the text. Release to re-blur.

Without JavaScript, I don't believe it is possible to preserve the
revealed state. If you find a way, please make a fork and add it!

Some systems will override color and text-blur styles on highlight,
but you could do that already anyway.

Author is using the Control Freak extension (http://goo.gl/QARGZ4)
in Google Chrome, however any extension that inserts CSS into a page
should work.

*/
span[style='color: transparent'] {
  text-shadow: gray 0px 0px 10px;
}

span[style='color: transparent']:hover {
  text-shadow: gray 0px 0px 5px;
  /* Changing the pointer might be too much, feel free to comment it
     out if you don't like it.
  */
  cursor: pointer;
}
 
span[style='color: transparent']:active {
  color: inherit !important;
  text-shadow: none;
}