one site many templates

hello

I have read some docs about theming in Drupal and view some modules for displying content but I have some question.

1. I would like to have one site on one domain but with some parts. How it can look like.
In the primary links I would like have something like this:

| Start | Library | Media | Forum |

So when I click on Start the default template should load and be visible, when I click on Library
the colors of the default template should change. So the shape of eg. header should stay the same but colors not.
More when I click on some links which are on the default page under link Library something like secondary links or links to some articles in library
color for library shouldn't change to default but should still be the same as for whole library. So when I read any article from Library the color
scheme is for library.
When I click on Media the color scheme should change to other from default and from library etc.
So every main area of the template should have their own color scheme.
How to create something like I wrote above.

2. Second question is:
When I am in Library link I would like to see default layout for this area, so when I click on one of the link in the main page
of Library I would like to change the layout eg. from 3 columns layout to 2 columns. So in other words
every area of this site should have their own main layout for the main area's page and some other layouts for sub-pages.

Any idea will be appreciated.