Before fans identified him as the Night King’s dragon, Viserion was one of three dragons given to Daenerys as eggs. Identified by his cream and gold egg and scales pattern, Viscerion was considered the friendliest of his brothers. When full grown, Viserion has primarily golden scales with creamy-white spikes, horns, markings spread across his body and tail. His wings had a more reddish-orange coloring along with Viserion possessing green eyes. He was also the clumsiest dragon, struggling to maintain proper stealth or temperament for patient hunting compared to his siblings.
After being turned into the equivalent of a White Walker for dragons, his eyes turned blue along with his scales gaining a blue to white color pattern. He also gained horns reminiscent to the Night King’s icicles. There was a debate about whether the Nigh King technically made Viserion a Wight-dragon but based upon the script for the Season 7 finale, it refers to the Night King as using the same process he used on Craster’s children for the dragon, which was different than a simple resurrection. It may also allude to Viserion never actually dying but instead maybe being close to death.
While Viserion is referred to in the Season 7 finale script as an “ice dragon,” he doesn’t fit the previous descriptions of an ice dragon. According to the books, ice dragons are made of living ice with pale blue eyes and translucent wings. They also breathe cold instead of fire.
It’s still possible Viserion became an ice dragon as the HBO viewer’s guide had it listed that Viserion was breathing freezing ice-breath although the script directly contradicts this by saying it was blue-colored fire.
Rumors state that Viserion may have become a new type of ice dragon caused by an unexpected mixing of the Night King’s magic with the innate magical properties of dragons. It’ll be interesting to see if the Night King applied other magical enhancements to Viserion to make him more powerful as it’s inevitable he’ll be fighting his brothers in Season 8.