@burcinc-- If you want to avoid damage to your hair, you could dye with henna. But I'm not sure if it will loosen them, so check with your hair stylist before dyeing your dreads.
I dye my hair with henna all the time, it makes my hair a nice red color. It fades over time, so I have to dye it again after a few months. I like henna because it's natural and doesn't contain chemicals.
Applying lemon juice to dreadlocks and exposing them to sunlight is also a good way to make your hair lighter naturally.