How can I change tab bar color in ConEmu

You can make the active tab more visually distinct by dynamically modifying its title.

Under Settings > General > Tab bar, you can set the Console setting to something like

%m< m%M(M%c%m >m%M)M %s

The %m...m block only appears on the active tab, while %M...M only appears on inactive tabs, giving you < 1 > Tab name on the active tab versus (2) Tab name on inactive tabs. You can customize this styling however you want.

Another option is to prepend the unicode character of your choice before the active terminal, like so:

%mm (%c) %s

Or

%mm (%c) %s

ConEmu does not have such option because that is standard Windows control. Just change your Windows settings (if you can).