One of the features that DialogueActions contains is the ability to load and change background images from a Dialogue.
This is done by setting the background variable, like so:
{"set":{"da.background.load":"filename.png"}}

The background variable should be set to value containing a name or path of a background image.
The FULL path is
(Loader.swf location)/Mods/(Last loaded CharacterFolder)/<backgroundvariable>
Just install DialogueActions in your $INIT$ folder.
So lets say you have your DialogueActions dialogue in a testing folder, called "LoaderDialogueMods".
And the loader is installed in a folder named SDT. What's above that isn't really interesting.
The path we'd be looking for would be 
SDT/Mods/LoaderDialogueMods/<backgroundvariable>

If you set background to "bedroom.png", the path becomes
SDT/Mods/LoaderDialogueMods/bedroom.png

This means that you should add a bedroom.png image file to the folder you store the dialogue that uses DialogueActions.

Triggers related to backgrounds are 
[CHANGE_BACKGROUND]
and
[FADE_BACKGROUND_<hex>]

If a line contains [CHANGE_BACKGROUND] or [FADE_BACKGROUND_<hex>], DialogueActions will store the value of the background variable in its internal memory, rather than directly swapping backgrounds.
When the [CHANGE_BACKGROUND] trigger is reached, the background will be switched.
When the [FADE_BACKGROUND_<hex>] trigger is reached, the trigger will be parsed.
The <hex> should be a 6-character hexadecimal string (do not put # or 0x in front). Examples: ffffff (white) 000000 (black) CF5300 (orange)
FADE_BACKGROUND will first cause a fade-in. The screen will quickly become the color dictated by the hex variable.
When the fade-in has finished, the screen will be entirely covered in the color dictated by the hex variable.
At this moment, the background is swapped.
Then a fade-out will occur. During the fade-out, the screen will quickly be restored to SDT.
During the fade-in and fade-out, the game is NOT paused. You can open the menu - this will pause the game, but the fades will continue.
The fade-in and fade-out take about 25 to 30 dialogue characters, depending on FPS. I suggest you use 30 delay characters if you want a dialogue line to be paused until the fading is done.
