John grasps in vain for words with which to give an accurate description of what he sees in vision. At first sight of the whiteness of the hair of the One appearing to him in vision the whiteness of wool comes to his mind. But no sooner has he written this than he thinks of an even whiter substance, snow, and he adds it for a yet more accurate description. Perhaps also, the description of Dan. 7:9 comes to his mind.
Flame of fire.
That is, a “fiery flame,” emphasizing the brightness of His countenance and the intensity of His gaze.