Upgrade was an Upgrade material option, an Alpha Quadrant Alliance designation for the visual appearance of a spacecraft's outer hull, i.e. a vessel's "skin". The Romulan version of Upgrade was available for some warbird classes of the Romulan Republic and its Romulan Republican Force. Upgrade put the ship in a multifaceted green cover, with panels of different shades. The warp plasma in the nacelles appeared bright green. (STO - From the Ashes mission: "Explore the Flotilla")
Related ship classes are sorted together, rather than alphabetically.