how to not fade dark colored jeans when washing,and prevent them from shrinking?
Turning your jeans inside out while washing helps keep the color.
Cold water and special detergent for that purpose. Don't put them in dryer.
Wash with other dark colored clothes with cold water and detergent made for dark washes, low heat dry and hang up to air dry when mostly dried
Wash colored jeans with cold water instead of hot... As for preventing them from shrinking, sun drying is the safest way to be sure...
wash in cold water and hang dry, only put them in the dryer to fluff them up after dried