Can anyone suggest a Firefox addon or greasemonkey script to change background??

[zyberboy]

I prefer grey or black background for webpages,white and high contrast light colors r hurting my eyes even though i am using Lcd monitor , i need a addon or script which will change the color of the webpage i am visiting with a shortcut key(when i press color changes) after loading the page or before(or having both option) , plz help.
Currently i am using a script frm *userscripts.org/scripts/show/6205 which only replaces white, not other light colors

 

[led_shankar]

Tools -> Options -> Content -> Click on the "Colors" button -> Uncheck "Allow Websites to choose their own colors"

 

[zyberboy]

But it will change to that color even if it is black background .I need a script that only changes light background or using a shortcut key to change manually.