I can avoid dark objects just fine, what is difficult to deal with is people who wear what could the equivalent of camo, and getting pissed that I didn't see them until late.
A tree is much larger than a human, making it more visually distinct.
Lets take an extreme scenario, just to try and find the limits of what is the responsibility of a driver and a bicyclist, I know it is a ridiculous scenario, but it is interesting to see were people feel the limits should be.
A person wears a ghillie suit, and lies down next to the road, he is playing a game of extreme hide and seek with a few friends, well the game day just ended, and he stands up just as a car is 50 meters away, the speed limit is 50kmh, it is dusk, the driver of the car swerves to avoid potentially hitting the person, and hits a light pole on the other side of the road.
Who would you say is responsible for the accident?