@Alex> thank you for the link. I gave a look and it seems that tool is only for APP Framework.
My new app is to be developed in Framework7. I found some pre defined themes (http://www.idangero.us/framework7/docs/color-themes.html#.VsHvPPIrK74), but I couldn´t find how to manage them or create a new one.
Good question. Framework 7 isn't really about customization - their focus is on native fidelity.
I think you'll have make a separate overriding style sheet that you include later in the head than theirs, and put your own overriding CSS in it.