Overuse of laundry detergent can be a big source of dulling colors, and it's not great for your machine, either, particularly with new front-loading machines. Try using half of whatever amount you're currently using — you'll be surprised at how clean your clothes will be.
Add lemon juice to your wash cycle to brighten whites. This can bleach darker colors, so keep it to whites only. Line drying in the sun is also a terrific natural whitener, popular everywhere in the world except the United States.
For both colored and white laundry, add vinegar during the rinse cycle to remove excess detergent.