Urth Net
Dream Fava's hair
Here are some quotes about the hair-color of the dream Fava. Descriptions of her hair color when she's not a dream projection are about her wig and don't count.
IGJ p. 194:
"The chamber that confined us was so dimly lit that I could scarcely make out its walls; but as well as I could judge, only Fava had changed at all. And even Fava had changed only subtly, for she had always seemed an apple-cheeked child just short of puberty, with long, light brown hair and a winning smile."
Hair color: light brown. Special circumstances: very dim lighting would make colors hard to see.
RttW p. 85:
He turned and saw Spider...in conversation with small girls in starched frocks...
He asked politely how he could find Hyacinth.
"Down there," the blond girl pointed. "She's down there like Spider and me."
The dark girl nodded. "Down there where you're going, and she can't ever come back. Take a cake for the dog."
Hair color: blond *Special circumstances: *dream on the Whorl, before he met Mora and Fava in real life. Is this a time-travel dream projection? I think so. The conversation indicates Fava and Hyacinth are both dead.
RttW pp. 23-26
"A little girl named Mora, and another one..."
...
"There was a little girl hiding under there already. At first I thought it was the one with yellow hair, but it wasn't." ... "Then I thought it was the other one, Mora. Only it wasn't her either."
Hair color: yellow. Special circumstances: this is Hide's dream. Hide is not as smart or observant as Silk.
RttW pp. 94-95.
The deadcoach dream. Mora and Fava are there, but no hair colors are described.
Given the evidence, I would have to say that the dream Fava was blond, yellow-haired. The only case where she is described differently is in the cell on Green, but that was in bad light. If so, we can only make her Hyacinth by dyeing her hair.