Doesn't work at all for me - no leaves turn white when snowing. See the screenshot below where I'm in a snowy biome while it is snowing and none of the leaves are white.

https://imgur.com/a/DVrHXSW

The leaves don't immediately turn white when snowing, they do take a bit. The speed is controlled by the randomTickSpeed gamerule. I personally find the default random tick speed realistic enough.

I knew someone would say this... Should have added that I did wait for several minutes. Not a single leaf changed colour. I have been sitting in a different snowy biome for 5 minutes now and all leaves are green still.