It turns out that that the atmospheric mix of Earth's surface (of N₂ and O₂) would naturally settle at the atmospheric column very near where the temperature is pleasant by Earth standards. Such floating colonies would basically be completely palatable by Earth standsrds (albeit perhaps with temperatures more reminiscent of Australian outback or Qatar than those of Europe or the US).

Floating colonies present their own issues, but it would solve concerns about long-term low-gravity impacts of Mars or the challenges of requiring a fully-pressurized environment suit all the time outdoors.