Question about a bullet

[Scott]

What is the green gel like line that goes around the bullet in this picture?

Does it effect the way that I'm crimping? Is it only for one type of crimp (roll vs. tapered) and shouldn't be used for the other? And finally, what is the difference between a plated bullet and cast bullet such as this? I understand that one has a jacket, but what exactly is the significance?

I've been using the Xtreme copper plated bullets and have had no problems with them except for an occasional mis-crimp(?) where the jacket peels back and bunches up around the brass lip. But I was looking for something that I didn't have to worry about the jacket bunching up and was cheaper.

TIA.