Whenever I shred potatoes for pancakes, they always turn ugly brown ...and for parties, I can't shred right at the last minute...what do you do?

In recipes including onions (not this), alternate grating potatoes and onions. That helps too. Squeeze well in a kitchen towel to remove liquid.

Shred them into water with some lemon/lime juice added. it slows down oxidation.

If you want to do them in advance shore them in water or you could bake potatoes the day before, cool them in the fridge then peel and grate. If you bake the potatoes it makes for a very tender rosti

Just use tap water. Cut potatoes, submerge in water and place in fridge till ready to use. They will stay bright and not turn brown or gray.