I have several black shirts that are still in good shape structurally, but they're quite faded. When I heard that adding coffee or tea a washer's rinse cycle would restore some of the color, I knew I had to try it. Today I rinsed black clothes with coffee to make them darker.
I didn't have a complete load of dark-colored clothes, so I decided to perform my experiment on a couple of black tee shirts. I wore one of them yesterday, so first I had to make sure it was clean. I got out a bucket, added some detergent, and hand-washed it. This shirt has never been treated so well! For comparison, I got a Mizzou tee out of my closet. The shirt is a few years old and pretty dingy looking.
I put both shirts in the bucket, poured a cup or so of coffee over the top, and agitated them with my hands until the coffee was incorporated. I let the shirts sit for a few minutes, then I squeezed all the excess water out and threw the shirts in the dryer.
I took them out when they were dry and hung them in the laundry room. I was pleased to find out there was no noticeable coffee smell. At first I didn't think there was a substantial color difference, but when I compared the "Before" (above) and "After" (left) photos I discovered the Mizzou shirt was quite a bit darker as a result of its coffee bath. The other shirt wasn't quite as faded to start with; its transformation wasn't as dramatic.
The darker color is temporary; it will rinse out the next time I launder the shirts. I can't see myself using a coffee rinse every time I wash something black, but it's nice to know how to do it.