I've installed two Nest thermostats and there's industry standardized color-coding and functionality and Nest conforms to that. (I don't doubt that you had that problem, but I think that speaks more to the incompetence of the original installer than to the complexity of installing a thermostat with a screen.)
I think it was more that the heat pump itself really wanted to be integrated with the Carrier Official Thermostat (which I think might have been an ecobee but can't remember), and the documentation on how to run it in legacy/standard/on-off mode was missing or confusing.
