I am trying to create/modify a color scheme for myself from the existing ones... But I am confused on the various different objects. Is there any documentation (w/ previews) of the various objects whose color can be set/viewed/modified?

Settings > Colors > Colors (tab)

For example, I am looking for a place/doc which can answer these type of questions (few examples):

1. What does "Focus Decoration" mean?
2. There is a search bar on top of System Settings window, which is "inactive / disabled" depending on the the context. Which color options govern this search box?
3. The background color for active and inactive tabs are different. Which "object" defines this?

The information here seems quite detailed and may help: http://techbase.kde.org/Projects/Oxygen/ColorSchemes

Thanks bcooksley for the link.
Yes, that is indeed detailed to some extent, but unfortunately my questions still remain a mystery, especially 3rd one:

3. Which widget controls the background color for active and inactive tabs, say in Konsole, Konqueror?

I've been playing around w/o success. And btw, there is a color scheme named "Zion (reversed)" which I don't see in the list of scheme under Settings > Appearance > Colors > Scheme.

another example:


Which widget color controls the "auto-completion" part of the text in krunner (which is barely visible)?

It is probably one of the text colours for the "Disabled" or "Inactive" roles, in the case of KRunner ( Inactive is most likely )

Haven't been able to figure this out yet Many of these are very very non-intuitive... Especially with a darkish color theme, it is becoming very difficult to get one thing right and not mess up the other....

You may wish to contact Matthew Woehike, who I believe is the maintainer of KColorScheme and has written many of the currently available schemes.