The player-character is the most important character in the game, so it is a good idea to spend some effort into making them look unique. Every creative choice about the look of the PC should be deliberate and well-justified.
However, hair color is not the only way to do that. There are lots and lots of details you can add to a character to give them some unique touch.
I would argue that giving the player-character a realistic hair color while giving some NPCs fantastic hair colors might in fact not be the worst decision, because it will make it easier for the player to identify with the player-character. For example, did you notice that anime and manga, the art style which basically invented the idea that every color of the visible spectrum is a natural hair color, more often than not use natural haircolors for the protagonist and unnatural colors for supporting characters? This serves two effects:
- It is easier for the audience to identify with the protagonist, because they are the most "normal-looking" person on the screen.
- Ironically, it helps the protagonist stand out, because they are the only character who does not have an unnatural hair color.