[HTC Desire S] madmaxx82:
Decided to answer in the thread instead in case someone else likes to know:

Creating a theme that can be used with 4EXT Recovery is not that difficult (except for making nice looking graphics and designing of course)

A theme consists of an icons folder containing your backgrounds/icons, a 4ext.prop file which includes settings for colors and tells the recovery where (path) to find the icons.

The easiest thing to start out with is to download a 4EXT Theme and extract it somewhere or use this template: flashable theme template

You will find the following folder structure:

system and META-INF

inside the folder system there is a subfolder called "4ext"

Inside "4ext" you will find a file called 4ext.prop and another folder called "icons"

Now -if you extracted a theme and didn't use the template- delete all png files inside icons and also delete the file 4ext.prop. Because you want to replace them with your own later on.

Now you need to decide about which standard recovery graphics you would like to change with your theme. You don't need to change all of them. You might only want to change the main background, that would work too!

To replace one of the recovery standard icons you only need to put your own png graphics file into the icons folder and name it the same as the original icon that is used inside recovery.

As an example for replacing the main background:

"icon_clockwork.png" is the main background icon's name.

Now if you want to replace the default background icon, put your png file into 4ext/icons and name it "icon_clockwork.png".

Your own png files should match the resolution of the devices you want your theme to be compatible with.

All devices supported by 4EXT Recovery at the moment use 800x480 pixels.

EXCEPT the Sensation which is 960x540.

Now for the other icons:

Here is a list of all of them that COULD be used or replaced by your theme:

icon_clockwork.png <- main background
advanced.png <- background to display when the user moves to or enters "advanced" inside recovery
backup_restore.png <- background for backup restore menu
ext3_4ext_ext4.png <- the 4EXT Menu's background
power_menu.png
reboot_now.png
toggle_usb_storage.png
icon_toggle_usb.png
install_from_sdcard.png
wipe_format.png
mounts_storage.png
icon_error.png

As you can see all icons are named after the corresponding menu option.

Here are some more "special" icons that are a bit more advanced, since they are of a special size. You can experiment with those or leave them be ;)

progress_fill.png
indeterminate1.png
indeterminate2.png
indeterminate3.png
indeterminate4.png
indeterminate5.png
indeterminate6.png
progress_empty.png

I've attached the original icons

So after you have placed all your icons you would like to include in your theme in the icons folder, it's time for 4ext.prop.

The 4ext.prop file for a theme is the same as the one in your sdcard/4ext folder, but WITHOUT any options that are not related to themes.

This 4ext.prop file consists of all the color and transparency settings and it tells the recovery where to find your icons.

You can use 4EXT Recovery Control since v2.1.0 to setup all your colors / transparency on the live preview screen.

When you are satisfied with the results use the app to export those into a 4ext.prop file which is then ready to be used in your theme zip.

But you can of course also edit the file yourself and mix the colors with any rgb(a) utility/website/whatever and then put those values into that file. (there is a link to a website in the 1st post where you can do that for example)

Here is a basic template:

bitmaps.usericons.sdcard.force=no
color.custom.sdcard.force=no
bitmaps.usericons.location='/system/4ext/icons'

selector.color.red=254
selector.color.green=43
selector.color.blue=0
selector.color.alpha=254

menu.color.red=0
menu.color.green=254
menu.color.blue=0
menu.color.alpha=254

text.color.red=0
text.color.green=254
text.color.blue=0
text.color.alpha=254

header.color.red=254
header.color.green=10
header.color.blue=0
header.color.alpha=219

You don't need to change anything, the path you see above: /system/4ext/icons is the path where recovery will find your custom graphics once your theme is installed. This path is always the same. The setting is only there for backwards compatibility with earlier 4ext versions where the path could differ.

You only need to modify the argb values for menu, text, selector and header to reflect the colours of your choice.

So by now you should have all your background graphics put into the icons folder and your custom made 4ext.prop file inside the 4ext folder (of the previously extracted theme zip file)

Now simply create a zip file out of that and you are basically done.

The zip file should be exactly like the one you extracted before:

1. folder system: containing a subfolder 4ext which contains your 4ext.prop file and the "icons" folder containing your icons

2. folder META-INF this contains the updater script that is run when your theme is flashed through recovery and not installed via the app.

You might want to edit that updater-script file and put in your own name ;)

Sorry this post is far from complete, but I hope it might be useful.