Black jeans look awesome when brand new. They have a slimming effect and appear more dressy than regular blue jeans. With a few basic steps you can keep those new jeans looking new without fading the colour.
Choose a good quality washing powder. Use one without bleach added and made specifically for dark clothes.
Turn jeans inside out. Wash in cold water instead of warm. Use the shortest wash cycle and preferably the gentle cycle.
Dry jeans on a clothes line instead of in the dryer. If necessary put in the dryer on lowest setting when damp dry; this keeps the jeans from becoming too stiff.
Use black powder clothes dye in the wash to keep the colour looking fresh. Add to the wash once a month or as needed. Clothes dye is available at fabric stores and most retail stores.
Do not hang jeans in sunlight to dry.