Putting different Theme is not possible, but tabs can have different styleboxes depending on their state, I think the latter is what you want?
Select your TabContainer, look in the Custom Styles section in the inspector: here you can choose which style will be used for each state of the tabs. Tab Fg is for the selected tab, and Tab Bg is for other tabs.
However if you want every tab to have a different color regardless of their state, you’ll probably need to make a custom control.
What I want is for each tab to have its own color. I chose to leave as is, thanks!