Why do they change colors? lol

I'm not sure on how IE8 chooses the colour, but when you open a link in a new tab the tabs are colour coordinated to show you where you launched the new tab from.For example in your picture the new tab "My Threads" has been launched from the "Windows 7 Miscellaneous" tab.

This is from Microsoft help - New features of IE8 "Enhanced Tabbed Browsing It can be difficult to keep track of many tabs at once. Internet Explorer 8 introduces Tab Groups, which make tabbed browsing easier. When one tab is opened from another, the new tab is placed next to the originating tab and color coded, so that you can quickly discern which tabs have related content. If you close a tab that's part of a group, another tab from the same group is displayed, enabling you to remain within the context of the current task rather than suddenly looking at an unrelated site. By right-clicking on any tab, you can close the tab, close the tab group, or remove the tab from a group. From the same menu, you can refresh one or all tabs, open a new tab, reopen the last tab closed, or see a list of all recently closed tabs and reopen any or all of them."

Thank You Very Much :)

You are welcome.