Why are some version numbers in TMS blue?

Because that version is out of date.

TMS will display Firmware and TMS Client version numbers using blue rather than black text if a later version is known to be available.  It's a gentle hint that you might want to consider upgrading.

TMS isn't smart enough to know whether or not you're using the latest version of a Long Term Stable release (currently 4.8.x), so if you choose to use LTS releases you'll have to put up with permanently blue Firmware Version text, and periodically perform your own check to see whether a later LTS version is available.