The truth is that everyone who peels potatoes has the same problem. By the time you put them in the pan, they have already started to brown. Of course, this has its explanation.
Potatoes turn brown quickly when exposed to fresh air because they are full of starch. When starch is exposed to oxygen, it undergoes a process called oxidation, which leaves your potato gray or brown. They are 100% edible, but less attractive.
The easiest (and most common) way to protect them from tanning is to use cold water. When the sliced potatoes are placed in water or even in a bowl with ice cubes in the refrigerator, the oxidation process is slowed down.