I tried to apply some of the themes from the list you linked and they don't work either. Same result as on the first screenshots I posted. The Carbon theme kind of does apply but now breaks when opening a system: I guess there's just something wrong with the package on AUR and I need to find some other way of installing the ES. Thanks for your help!

@Crispy The only change that would affect this should be the changes in Emulationstation. The desktop - I assume - is only started on-demand. You can take a look at the theme - it's in /etc/emulationstation/themes/carbon. If you wish to modify it, copy the folder to $HOME/.emulationstation/themes/carbon-mine and make your modifications there.

I have the same setup as you (mostly) and had the exact same problem. Do what @mitu said, set gpu memory split to at least 256MB.

That was it! So it seems the selectorColor property is a multiplying value. Regards and thank you very much. EDIT: You can see the result here ...no I can remove the UP/DOWN help from the bottom.

Those are just warnings, they're not errors - it's safe to ignore them.

@ciofalello That's not all the information asked in the page. What is your Video RAM limit in Emulationstation ?

It worked thanks guys:)

@dal1980 While you're developing your theme, it's good to start ES with the --debug flag and look in the log file to spot any errors coming from the .xml files parsing. The log file is in /home/pi/.emulationstation/es_log.txt.