SnugZero100% Cotton Lattice-Knit Skull Cap Beanie Kufi | Solid Colors and Cool Designs for Everyday Wear

why is there a size chart if it's only one size fits all?

I have this cap in grey and dark grey. is the green cap a very dark, subdued near-black green, subtly colored like the dark grey one?

Will it protect a bald person from the sun?

I purchased the black one. Can this be washed in washing machine (if so, warm or cold) and dried in dryer?