liver spots?

[cmbyrd50]

Hello All,
I have a question maybe someone can answer for me.
You know the marks people get on their arms from either bunking them or
a dog scratching you anything that's got some weight to it? Usually
this happens to older people.
I've read in the past that darker colored marks are caused from the
liver and the lighter ones being the kidney.
Does anyone know which it is?
Thank You
Colleen