Change color when the character is hit.

The truth is that I have many problems with this, I want the character to change color when it is hit, but I don't know where to start.

I know how to change the color of a material, but I don't know how to change the color of all the materials of a character and that they can then return to their original color, I don't know if this is done by changing the materials or in another way. Can someone help me?

Thanks in advance