This issue is not new and has been there for FCK too if you had set dynamic stylesheets (meaning it would load skin.css).
Seems like RadEditor does this by default.

I don't agree it's a Core issue, it's an issue of the skin as there is a simple solution.

Most editors are shown in an iFrame and the content of the iFrame contains a body tag, just like the DNN page itself.

If you want a WYSIWYG experience in the editor it has to load skin.css, so it will also show the page background (if was not set correctly)
To make a distinction between the body of the page and the editor, the main body tag of the DNN page has an id #Body, which the editors don't have.
This id is there to prevent these kind of issues.
So you can use #Body {background:#F00;} to set the background color in skin.css.
As this ID is only there in the page body tag and not the editors body tag, only the page will get a red background, not the editor.
That should eliminate all background issues with any editor (as it's very unlikely it will inject this id in it's body tag)

For an example take a look at Skin.css in minimal extropy:
#Body {background:#FFF url(images/body_bg.png) ...........}
You don't see the blue background in the editor on the forums right?

A good skin should use #Body{...} and not body{...}

The "solution" is very simple has been posted to this forum lots of times and and it does not get lost on DNN upgrade, unlike many other solutions I have seen.

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Lindsay...I see you are running 5.5.1... do you have issue with linking pages using the RAD editor? I cannot get the link manager to work correctly. I can specify URLs, but cannot select pages inside the CMS?

I know this is off topic, but you have the same setup as me... I posted this issue here: http://www.dotnetnuke.com/Community/F...

If anyone can chime in on this it would be great...