Brief introduction
All sets of skins are stored under the directory:
<123flashchat installed directory>/client/skin/.

By default, we offer eleven skins. You can modify these skins or add your own based on the pre-existing skins.
Skin components are controlled by skin.xml.
Color style can be adjusted by color.xml.
skin.xml and color.xml are located at <123flashchat installed directory>/server/etc/groups/default/skin/skinfolder/
Only SWF or JPG image file can be used to construct a skin.
If you like the opaque background, you can save it as a jpg file (non progressive mode). If you would prefer a transparent background, please save it as a png or gif file and import it to flash to convert it to a swf file without background.
Client FLA files are not necessary to design a skin.

Below are some tutorials which might be helpful for designers:
a) How to customize skin? http://www.123flashchat.com/howtoskin.html
b) How to change skin color? http://www.123flashchat.com/colormap.html
c) How to customize the background? http://www.123flashchat.com/howto_change_bkground.html

Change background
Every skin offers background pictures in the chat area.
You can also create your own jpg or swf backgrounds and put them into the skin folder. New backgrounds should be in the dimensions within the basic background. The graphics for the new background will be added above the basic background. (We suggest you double-click the background alternative in the download pack to get a better picture of how it should look like.)

To offer more backgrounds for users to select, please edit skin.xml,
Find the following section:
<SKIN_BKGROUND>
<BKGROUND name="Standard" value="bkground.swf" />
</SKIN_BKGROUND>
Then add a new line in this format. Name is for users to pick from. Value is the filename of the background that you have created.

To learn more, please here.