These are awesome. I recommend getting the mulit-color ones as you can have any color you want then.
Power button turns them on, then as it rotates to the color you want, press the power button again and it will stay at that color.
I bought 3x4-pack last time, and I will buy another 3x-4 pack this time. I use them for camping and while walking my dog. One AA battery will last about a month with about 3-4 hours use a day.