I just ran into a problem where the characters fingernails were a dark brown colour. After much searching, I found a solution and thought I would share it in case anyone else runs into this.
First, this is the problem...
Go to Surfaces tab -> CharacterName -> Surfaces -> Fingernails.
When there, scroll down to Translucency Weight (or search for Translucency Weight in search box)
Lower the Translucency Weight until it looks good (this varies, 0.25 worked for me the last time I did it)
You can also copy fingernail from other characters to fix it, but this method preserves the character's original materials.
This was the setting before I changed it...
I lowered that to 0.25...
And this was the result...
Much better. I see this every once in a while and thought I would share my solution.