It is possible to create and use custom themes in Fiery Feeds right now. It is a somewhat complicated process, but improvements are already planned for a future release.
You’ll need a text editor to create or edit the theme file and a web server to install1 it. Installation will be improved in a future release.
The theme file
The theme file is a simple JSON File where every value is the hexadecimal representation of a color unless otherwise noted2. You can take a look at the default Light Theme to see how it should look like.
Installing a theme
To install the created theme file you need to upload it to a web server3 and create a link in the form of
fiery://addTheme/ and append the URL encoded link to your new theme file. Then simply open the newly created link in Safari on your device to launch Fiery Feeds and install the new theme.
The following shows which values control which elements. Note that all colors other then
navbarTitleColor default to black if they are not present in the theme file.