Once I get gray hair dyeing done, do I have to get it done frequently?

As I get older, I notice one or two gray hairs every time I look in the mirror.

It stood out. I didn't really notice it when I called my head, but

I tend to have some gray hairs visible from the side when I tie my hair back. I'm thinking of dyeing it if it progresses a bit more.

What I'm curious about is how gray hair dyeing is different from regular dyeing.

Also, I'm wondering how often I need to receive it once. And lastly, I'm curious about...

There are a lot of gray hair shampoos coming out these days, too.

I'm curious how effective this is too.