Programmatically coloring sprites

I have this tree sprite:

I'd like to create a script that makes the green parts change their colors for another three colors.

I don't know how to start, as I can't run a for loop without breaking the game and I read that if you change the color of the sprite, you change the color of all trees that use that sprite, and I don't want that.

What approach should I use to do this (in Start() if possible) ? Thank you !!!

 

some options
- make them as separate sprites (then randomly pick different ones)
- use grayscale tree parts, then adjust sprite color to color them
- palette swap https://www.assetstore.unity3d.com/en/#!/content/8649, free alternatives, https://github.com/tutsplus/Dynamic-Sprite-Color-Swap-Shader and more