When you expose a potato's flesh to the air, whether by peeling, chopping, slicing or some other means, it will begin to oxidise. While this will not adversely affect the potato's flavour, it will cause unsightly discolouration. In extreme cases, the exposed flesh of the potato may even turn completely black. This can complicate any attempts to peel and partially prepare potatoes in advance. With a little foresight and preparation, however, you can keep your peeled potatoes light-coloured and fresh overnight.
Add enough water to a large bowl to completely cover your potatoes. Do not put the potatoes into the water yet, however. Add the lemon juice to the water and stir well to blend.
Peel one potato, then place it immediately into the bowl of cold water. Repeat this process until you have peeled all of your potatoes and put them all into the bowl.
Check the water level to ensure all of the potatoes are completely submerged. If they are not, add more cold water until they are, then cover the container.
Put the container of submerged potatoes into the refrigerator overnight. When you are ready to use them the next day, they should still look as fresh and light as when you peeled them.