Change players skin color

[Zero Human]

I have all chars with brown skin colour, but I don't want to replace all chars with brown skin colour,

but let the player choose if he wants to have white or brown skin colour.

Is there a possibility to call both sprites separately?

 

[Waken]

They are not sprites but palettes, so in your data/grf you need to have palettes for both (brown and white), you can manage it by ranges. (1-100 white 100-200 brown).
And then modify your stylist npc to let the players choose if they want the brown skin or the white.
Sadly the cloth colors and the skin are not separated because they are an unique palette (as you see in the image below) and this is hardcoded in client.

(old image from the hercules wiki)