Part of climate change is that the Earth’s albedo is heading in the opposite direction — as the ice caps melt, less light gets reflected into space, more gets absorbed.

It feels like you’d need to lighten the Earth’s surface a lot just to counter that effect, let alone mitigate warming from other causes.

On a local level, this can work well to keep a town/city cooler. I’d plant greenery as well rather than just paint roads white though.