The darkness is easy enough to fix: Just turn down the opacity a bit. I agree with - Max -: at the size you're going to be showing these, the simpler icons will work better. Do a Google Image search for Pete Fenlon and check out his hill symbols. His mountains are a bit complex, but his hills are so beautifully simple.

I do still like those sketchy mountains, though, especially the gently sloped ones with the smudgier details. They may not work for this map, but I hope you find a place for them in another.