Kallorian

My assumption is that Harmony is not what we'd consider a new tone. Whatever tone Harmony has is both a combination of Ruin and Preservation AND something new, similar to how towerlight and warlight are both combinations, but more, likely with properties not entirely defined from either. In this case, the catalyst would've been Sazed. Likely a more spiritual catalyst rather than the physical catalyst of making a tone that allows them to combine.