It's fitting that Viserion has gold-colored scales and red-orange wings, given that he's named after Dany's brother Viserys (who, as we all know by now, is covered in gold himself). Like Rhaegal, we don't get to see as much of Viserion as we do Drogon, but we witness him doing his thing in the season five and six scenes in the Meereen catacombs (he's the one who breathes some pissed-off fire at Dany after she chains them up).
Since the White Walkers are marching into Westeros, Viserion has become the problem child of the family. After being resurrected by the Night King, Viserion's eyes turned an icy blue and he now breathes blue (still hot) fire. Technically considered a wight, Viserion has awoken as part of the Night King's army because, in this show, not even the dragons are safe from being pitted agains their own families.
