Hi hi, sorry to butt in, but since I was the one who asked this artist to draw them in my designs, I think I should explain about Celegorm's hair color.
I'm Japanese, and I happen to read the translated version of Silmarillion (as well as the English one) here, and the translation is sort of bizarre. Like you mentioned, I can totally understand how "fair" =/= blond; i'm sure it can refer to as having good looks.
However, the person who translated into Japanese happen to write "Celegorm the fair" as "金髪のケレゴルム", which literally means Celegorm the "golden hair"... so I guess I was greatly influenced by this, and the idea that Celegorm has golden hair got attached in my input.
In addition, just to let you know, the translated name for "Caranthir the dark" is "黒髪のカランシア”, which is.... Caranthir with "black hair".
I don't know why the person translated this way (I find it weird too.)
Hope it clears things a bit about "why Celegorm's hair is golden in this pic"