You have not stipulated wood. Hence, I am going to nominate graphite re-inforced plastic. The fingerboard of my Chapman Stick (see avatar) is made of the stuff.
Not a fan of unfinished/untinted maple, light hued rosewood or typical pau ferro...aesthetically they are a total turn off. I avoid them like the plague.
I hate light colored rosewood, otherwise I'm pretty much good with any fretboard - assuming it is done correctly and feels right. I am a fun of untraditional woods being used as well.