Understanding Themes in 2.0b5

I really like the new theming system, but I haven't seen a full explanation of it. Here's what I can deduce from experimentation. Hopefully this will be of use to other themers.
Please let me know if I got anything wrong.
This information is the best I can figure out from version 2.0b5, but I can't guarantee that it will stay entirely the same for future betas.

The Platform/Menu has both Built-in themes, and the ability to install Custom themes.
The Built-in themes are not really intended for editing.
Custom themes can only be installed one at a time.
Selecting themes is done through Options>Theme, which displays a long list of built-in themes, and at the very bottom, three small dots...
To install a custom theme, click on these dots and browse to your custom *.patheme file.

-The Built-in Themes:
While the built-in themes are not intended to be edited, you can get an excellent understanding of the system by examining them.
The new theme system uses layers of .png files and html colors to achieve a color-mixing effect.
It will be pretty powerful once it's finished, but themers will need to understand exactly how it works to use it to its best advantage.

The two layers for the background are:
- background.png
- the "chrome" files: white.png, dark.png, white_opaque.png, dark_opaque.png

There are also a lot of small .png files for the buttons and icons.
The html colors, choice of background and choice of "chrome" are set in the patheme.ini file.

First, let's look at the file locations.
The built-in themes locations:
X:\PortableApps\PortableApps.com\App\DefaultData\Themes\subfolders.
Each of these subfolders corresponds to one of the built-in themes in the list Options>Theme
The base of all of these is the Default folder.
It includes all the button .png files, including a subfolder called menu_icons that has the icons for the buttons in the right pane.
There's also a patheme.ini file, that defines the html colors, "chrome" and background.

Now, if you look in the other folders, you only see a patheme.ini file, except for Rainbow and Textured, which also have a background.png file.
When that theme is selected, whatever's in that folder overrides what's in the Default folder, but leaves everything else alone.
So, for example, in the Green folder's patheme.ini file, the [menu] section specifies

Chrome=white
Background=none
BackgroundColor=182802 ;GREEN

While in Textured Dark the patheme.ini file has

Chrome=dark
Background=custom

Here, the background color doesn't show through, so it doesn't matter.

The last piece of the puzzle is the "chrome" files. These are here:
X:\PortableApps\PortableApps.com\App\Graphics\Chrome
These .png files are the basis for the real look of the built-in themes.
They currently cannot be changed or added on to.

The color-mixing comes from the fact that .png files support transparency.
The "chrome" files and many of the the button files are partially transparent.
The menu layers them in this order:
TOP - "Chrome" file
MIDDLE - Background.png
BOTTOM - HTML color

So, that's how it works for the built-in themes. It's not recommended to directly edit these.
You CAN'T edit or delete the list of themes that appears in the list Options>Theme. It's built into the platform exe file. You're stuck with that list.

-Custom Themes:
Making your own theme uses the same concepts, but the files are in a different location.
There are also a few tricks that make theme creation easier.**

Custom Themes automatically install to X:\PortableApps\PortableApps.com\Data\Theme
You can build one directly in this spot, and then package it really easily.
Whatever you put in this location will override the default theme.

**TIP - First, we have to install an initial custom theme, so let's package a simple one to use.
Copy the default patheme.ini file to the X:\PortableApps\Documents folder.
Zip it.
Rename the zipped file to Base.patheme (make sure you replace .zip with .patheme).
Now, to install it in the menu, choose Options>Theme>...
Browse to Base.patheme, and Open it.
It won't look any different, but now we can play with it.

Here's some examples of custom themes.
We'll be editing the files in X:\PortableApps\PortableApps.com\Data\Theme
1. Special color
Edit the patheme.ini file [menu] section:

Chrome=white
Background=none
;BackgroundColor=550004 ;RED
BackgroundColor=7FFF00 ;Chartreuse

Save the file.
Close and reopen the menu to see the new color.

2. Special background with default "chrome"
In your favorite graphics editor, create an image 406x573 pixels.
Save it as X:\PortableApps\PortableApps.com\Data\Theme\background.png
Edit the patheme.ini file [menu] section:

Chrome=white
Background=custom

Save the file.
Close and reopen the menu to see the new background with the default white "chrome" overlay.
**TIP - if your background.png has any transparent areas, the BackgroundColor will show through.
If it has partially transparent colored areas, these colors will MIX with the BackgroundColor!

3. Total conversion
Copy all the files from X:\PortableApps\PortableApps.com\App\DefaultData\Themes\Default and put them in X:\PortableApps\PortableApps.com\Data\Theme\
Now you can edit these files in the new location to your heart's content!
Edit the patheme.ini file [menu] section:

Chrome=custom
Background=custom

Save the file.
**TIP - It's best not to change the dimensions of the different .png files, since that's hardcoded into the menu, and you can't relocate buttons.
**TIP - In creating/editing the .png files, there's a special color that generally displays as transparent - FF00FF. It was used in the old themes to make rounded corners, but with the new system, it can cause some weird effects.
**TIP - You can emulate the "chrome" file, sort of, with your background.png, if you make it grayscale and partially transparent. In GIMP, try reducing the opacity of the layer to 50% before you save. Then the BackgroundColor will show through...
You will need to restart the menu each time to see your changes.

Once your custom theme looks right, then you can package it easily. Select all the files in
X:\PortableApps\PortableApps.com\Data\Theme\
(don't select the actual Theme folder, though, just its contents).
Zip it.
Rename it by changing .zip to .patheme, and you are done!

This information is the best I can figure out from version 2.0b5, but I can't guarantee that it will stay entirely the same for future betas.

EDIT: I've started a site to share and host themes as 2.0 progresses.
It's here:
http://paskins.sourceforge.net/
I've got one of mine up there, and a GIMP template, but I'm OK with adding other people's themes.