What Am I Riddles

Question: I come in many different colors. I create boundaries to keep things concealed and safe. My best friend is a lock and I am also made of different materials as well. I love to travel: you can find me anywhere. What am I?

Question: Those who make this item, don't use it. Those who BUY this item, have no need for it. But those who USE this item, never see it. What is the item?

Question: What can be white and yellow at the same time?

Question: A powerful spell, the naive knows it well; one cast at an affair for your most popular gown. No sticks, no stones, a mage sans tomes, a fight, no toil but it still breaks you down.

Question: My thickness is no more than a few centimeters, yet my depth can span to infinity. Although mundane, I intimidate most animals. When in my presence, you will inevitably follow me. What am I?