Long story short injuries have specific color rations in this world,

Orange = mental
Light green= emotional
Pale blue/icicle blue= physical

It's extremely rare for someone to not have any injury mark on them, let alone only one of any of the three, the marks can only be obtained via human actions, so if you're hurt by a horse it won't show but if another human injuries you, a pale blue/icicle blue mark will appeared at the area, and depending on the severity it can range from the shape of a bruise to the shape of scars.

An interesting fact is that animals that have been harmed by humans will have their fur/skin change color to match the areas the harm happened at and the severity, allowing animal abusers to be less prevalent in this world. (probably one of the few good things about this world)

Little fun fact: I actually plan to try and write my first non-sander sides ship book with this AU in mind, One of the two main characters is going to have their body littered with the physical injury marks due to bullies in school, have a few emotional injuries, and a few mental ones (some of which being from the main characters parents)
The other will have a pale blue/icy blue image in the shape of a Vine on his face (it's rare when these happen but they can happen, this mark indicates that someone pushed this character into a thorn vine, hence why it's pale blue and shaped like a Vine, as a human caused this injury) along with a few emotional and physical injuries around the elbows and hands... I won't say the name of the ship but I will give a hint, cat hero. I hope you get it. Also please tell me if you want me to make this book because I will