Changing the appearance of the question title and tags

I am planning to change the following :

Color of the title of the question (both in the lists and on the question page)
Appearance of tags. Currently the tags are shown in a rectangular boxes. I want to change them to rounded rectangles with different fonts and colors.

What are the color names (in style.css) and parameters that needs to be changed ?

Just open your "developer tools" in the browser, find the element you want to re-style and come up with css for that.

You can test out your new style right in the "developer tools", css section. Then when you're happy with the new settings, create matching rules and add them to file "/media/style/extra.css" of your theme.

If you are planning small tweaks - do use the "extra.css" trick, it's described in the "customizing skins" manual.