Distinguishing between optical absorption due to polaronic states and free carrier effects such as the LSPR we observe in tungsten oxide NCs is difficult, but we investigate the extent of charge localization to provide an indication of which mechanism is contributing to the decreased transmittance of tungsten oxide NCs during electrochemical reduction. Specifically, we look to better understand the electrochromism of tungsten oxide by comparing the electrochromism of hexagonal cesium-doped tungsten oxide NCs (Cs:WO3 NCs) reduced in electrolytes containing cations of varying ionic radius. It has been previously shown that the coloration efficiency of monoclinic WO2.72 NCs could be increased by selective intercalation into larger interstitial sites using sodium-based electrolytes compared to electrolytes based on smaller lithium cations. Sodium ions were inhibited from occupying the small trigonal sites, which contribute only weakly to the optical response, improving the coloration efficiency. Similar results have been shown for hexagonal tungsten oxide nanorods, which showed variations in the amount of achievable coloration based on different surface faceting of the particles which varied the amount of accessible sites for lithium intercalation. Here, in Cs:WO3 NCs we reveal that site-selective occupation of interstitial sites based on differential cation size can tune not only the magnitude of the coloration, but can also give rise to dramatically different spectral signatures. We assign these distinct spectral responses to either plasmonic or polaronic absorption, based on extent of charge localization.