Hi, I always wanted a different look from default oxygen, mainly with these modifications:
-Dark titlebar/menubar/toolbar.
-Colored tool panels.
-Removal of extra lines and clutter.

I tried a lot with qtcurve and bespin, but couldn't do it and neither I could get the level of polish of oxygen (if you know how I would be glad), so I was thinking of modifying oxygen source to allow these modifications (I know some C++, yet I'm not an expert). How should I start? I couldn't manage to find the main oxygen github repository, are they still in svn? Is there any documentation on theme creation around? or of oxygen basecode in particular?

Also, how does qt5 change things? I read from hugo that oxygen works on qt5, so I assume kde5/qt5 apps will be styled like todays apps (C++ drawing the widgets). Or will they be styled on some qml widget engine totally different from oxygen code?

As far as I know oxygen is in the kde-workspace repo.

For Qt5, there's a few things. On one side, with Qt5 / KF5 not suddenly all apps will use QtQuick to draw their UIs. I would expect that to take at least five to seven years. Most will still be based on widgets. After all, there's nothing wrong with Widgets, so there's not really a reason to port away from it for most people.
Additonally, if I'm not completely mistaken, you can use Oxygen as a style engine for QtQuick Controls right now, which is what I think the plain for KF5 apps using QtQuick Controls right now. Whether that will be the final solution forever I can't tell (I don't even know if it's planned as such or considered an intermediate solution), but for the next few years I think it'll work.

Greetings,
Sven