Just use the set material node to change the material to a white one. Now activate it when you hit the character → hit - changes the material to the white one - delay of some seconds - another set material node that changes the material back to the normal one 
I am going to do material effect, When I hit monsters,
I went to monster’s material became white-color base(like some PC-online game),
help to do it, I have tried 2 days, I have no idea, Please help me, thanks.