If you've customized you Joomla site with a theme that has a dark background, you may find that your TinyMCE or JCE editor background is also dark now.  Here are some tips to get the editors back to normal:

JCE:

1. go to JCE Administration
2. Open configuration>formatting
3. Use template CSS, Set to NO
4. Save and exit

If problem still persists, set the "editor content class" to high contrast.

TinyMCE:

1. Go to Extensions » Plugin Manager 
2. Open Editor - TinyMCE 
3. Under Plugin Parameters, set Template CSS Classes to No. 
4. Save and exit

If you still want to theme the editor, but just want the background to be white, you can do the following in your template css files:

1. Change the "Custom CSS file" to "templates/$template/css/editor.css"
2. Then edit the template CSS file "editor.css" in the template manager by changing the "background-color: #[artisteer value];" to "background-color: #FFFFFF;" 

Editor background is now white.