Help me with the rep system!

Sorry for the thread. But I was unable to find anything that can help me on this.

I've got rep on my account from different users. But only one of those added to my rep. It shows a green box in front while others show grey. Why is this so?
Also,I'd like to know if the increase varies with rep from different users?

They lack reputation power to positively net you reputation points.

You gain reputation power when your reputation increases.

There's also other factors like time since joined, number of posts etc which should factor into your reputation power increase.