[Deidara837]

Reversing the tree:

The event (tree falling) should be observed (hearing it) if you want to confirm its existence a la Schrödinger's cat, otherwise the two possibilities can't be distinguished

Regarding perceived color I'm gonna back up rushy on this one - people wouldn't be able to perceive any colors (radiation reflected from an object reaching the retina), but materials may still retain their spectral reflectance properties. "Colors" themselves would still exist if you define them according to their electromagnetic wavelength, they just wouldn't be distinguishable without any light (electromagnetic radiation) to observe. But in the case that there was never any light, they'd be similar to an existence possibility that may come about but is never observed.

Musings as a color science PhD student