I've been playing with tweak for about an hour and (mostly) love it - I can't seem to figure out where a few things are set. The background for the minicart, the background for the selected category, and how to set the color of the buttons that are dynamically generated (I may just create my own graphics, but for now I am trying to change them.)
Also - the "manage" tab left me a bit confused... when I tried to save my new "tweak" - it ended up that I abandoned the changes I'd made and created a new tweak from a generic default store style... I was able to fairly quickly re-make all my changes, so it wasn't a big deal, but a "save current tweak as" choice would be great.
Cass Gerling commented
I really like this tweak program and I'm excited to see new additions and helpful tips soon! This is definitely a program that I would pay for.
Thanks for the feedback. The Tweak service is not well documented at the moment, and that is something I will improve before the end of the beta phase.
The minicart and buttons are all images, so to change their colour, either load in your own images, or go back to "Themes", make one with the colours you like, save it and use the "copy to CDN option to make it available to your tweak account. You can then select it from Manage > use saved theme.
Any time you click the "Save" button your Tweaks will be saved to the active Tweak (by default this is named "current". I think you may have created a new Tweak from the "manage" tab, but the previous one should still be there, probably called "current" and you may be able to select it from the "load different tweak" drop-down.
I hope to add more tips, help and documentation soon. I know it is a bit confusing right now.