A gas giant with a color-chemistry class of Sulfammic would likely have a vibrant yellow hue. The presence of sulfur in its atmosphere would give it a distinct color, reminiscent of the element's characteristic yellow shades in various compounds. Sulfur compounds are known for their vivid colors, and on a gas giant with a Sulfammic atmosphere, the swirling clouds of gas and storm systems would likely create a mesmerizing yellow and golden color palette throughout the planet's atmosphere. Overall, this gas giant would be a striking and visually stunning celestial body, standing out amongst the darker and more muted colors of other gas giants in the universe.