You can also get blue and white, red and white, and gloves that are the colors of the U.S. or Mexican flag, to mention a few. What color you get is up to you. My friend has a forty-pound bag she said she would give me. If you are getting it for free, go ahead and accept. You can always get a heavier bag later on.
Smaller bags are a little harder to control because they swing around more.
If you work out with a buddy you can take turns holding the bag for one another. If you work out alone you will get used to controlling the bag. For instance, if the bag swings to the right, stop it with a right hook and vice versa. I bought a heavy bag and hung it up in my bedroom. I'm really into punching it, and I can't believe how quickly I've gotten lots stronger.