How to create themes (or at least edit them) for this device?

[BasicallyCP]

Remaining somehow unsatisfied with the available (free and paid) themes, I actually wonder how to edit lets say the background of the menus or the font colour by myself.

I mean, there are some great creations available but their numbers are small (new device, ok, that might change) and with every one of them I found things which don't look good or are less useable than desired and would require only small changes.

This is not to criticize the creators of the current works but mainly a plea to receive some kind of tool or help regarding small changes to an existing theme. Other than the icons or the wallpaper, the phone's apps don't allow for changing much.

So, to list:
- Change menu background
- Change font colour, perhaps text outline (mainly in menus)
- Change transparency of widgets
- Change colour of "enabled" vs. "disabled" sliders and buttons
- Change icon style (means if they are round, squared, etc.)

Things I've found so far, which may apply to the G7: How to change the nav bar colour. (that's a link from the mini review)

Edit:
Would SystemUI Tuner help? From the description, it does touch on UI items (hence the name) but wouldn't allow for the changes I've listed, no?