It looks like the border color corresponds to the grimoire value of the card: 5 point cards have the white border, 10 point cards have a purple border and 15 point cards have gold. Some cards increase in value as you meet the conditions to gain their bonuses.

I would like to know too. I hope Bungie can respond back cause the one have a yellow bar don't show points earned such as the Traveler grimoire card.... etc

I would really want to know as well, I've asked my friends and they had not even notices that difference. I've notices that some of them are white and some of them purple, but I've also noticed that some of them have the yellow bar at the bottom and some of them have a white bar, and it does not matter of which color the border is or the backroung all of them look kinda different. Initially I thought it was because of the games or things I had and enemies I had killed and what not but then I realize that some of them even though I had played already it was still marked different ways... If someone actually knows why I would love to know as well :)

Because Shineys!

I am new to this. What are Grimoire cards? What are they used for? Please help.