Ange's current appearance was indeed perplexing. A greyish-white skeleton, who could tell he was a Golden Skeleton?
Having a Soul Heart makes one a Golden Skeleton, but the metallization of the skeleton needs a process. Moreover, Ange's situation was rather special, the skeleton he now possessed was found in the Resting Camp, it was not normally evolved.
Besides, the process of his Soul Heart condensation was also special, directly condensing a Soul Heart at the stage of an Ashbone Skeleton, skipping the stage of the Silver Skeleton, so for him to metallically transform into a Golden Skeleton, he needed first to enter the silver stage, before transforming into gold.
Of course, terms like silver and gold were just common names, named according to the color of the skeleton. The correct terminology should be Lord Level and King Level, Silver Lord and Golden Skeleton King respectively.