Hey Alison, great question. We talk so much about investing in clothing that will last, but talk little about how in fact to make that happen. First I'll answer a few follow up questions, then get to the solutions.
Why do clothes fade?
Dark colored clothing get to that shade from dyes (no surprise there). When washing clothes, if the water is left a different color, it is because of dye being released from the garment itself. This is how whites get not-so-white, and the reason behind the red sock turning clothes pink phenomenon.
When washing clothes in water with detergent, this will happen over time. Some people turn garments like dark jeans inside out to preserve color. In all actuality, this doesn't preserve the die on the inside, it is only to prevent against the middle spin thing of the washer from causing abrasions... thus wear and fading. If you have a front load washer, it's less of an issue.
Also, the sun, hair products, and other chemicals can all lead to wear on the dye and how it relates to fiber, just as it can to your hot new hair color.
And what can I do about it?
-Hand wash with soaps made for dark clothes or Woolite. The dark clothes detergents actually have a small amount of dye in them to help restore the color, but this isn't such a great option if you have patterns on the clothes, because it ends up dying all colors, not just the black.
-Wash only with other black clothes. Remember the dye in the water I mentioned earlier? If you're washing all blacks together, this dye leakage that you are soaking in can help lead back to the garments that it leaked from. It's not really a fix, but it may help prolong fading.
-Dry clean. There's no water or color leakage here. So if your garments can be dry cleaned and they are worth preserving, this may be the route. You can also spot clean as necessary. Some people only dry clean their denim, particularly denim of the selvage variety. But that's another topic for another day.
-Dye the clothes to intensify the color. You can pick up a box of RIT dye from your local craft, fabric, or art store for a couple dollars and follow the directions to dye the entire garment in hopes of restoring the color. This method works best on natural fibers (cotton, wool, etc.), but can be used on synthetic fibers as well. But the same rule of thumb with dye applies: don't use it on patterned fabrics because it will change all colors, not just the blacks.