What causes gray hair in young age?

I like coloring my hair from time to time but still that gray hair can't be colored!

Is it possible that coloring increase the number of gray hair?

Or it's a genetic factor?
What is the best hair coloring product to cover gray hair?

You might want to go to a salon and have it dyed. This may help with your gray hairs and sometimes gray hairs are caused by stress or genetics.