How to Keep Composites White?

I have 2 composites on the corners of my 2 front teeth, and 1 in the bottom row towards the back. I'm still confused about my options for keeping them white. I just used some over-the-counter whitening strips and I know they are not supposed to work on composites, but they did either whiten them, or the composites just have not become stained yet (they are about 7 months old), because all my teeth look pretty white now. n the future, if I get my teeth whitened professionally in a dental office, will it keep my composites white?