Washing your 501 jeans with vinegar is a great way to maintain the original color. You need 1 cup of vinegar in addition to regular laundry soap. Schedule 20 minutes of soaking time along with the wash cycle.
Turn the jeans inside out
The physical wear of being agitated in the washing machine fades the color of denim. Likewise, denim tends to bleed color, so always wash jeans with other denim.
Soak for 20 minutes
Add the jeans to a tub full of cold water. Add 1 cup of white vinegar to the water to set the color.
Rinse out the vinegar
After the soak, rinse the jeans with cool, clean water.
Fill the tub before adding the jeans
Laundry detergent and fabric softener can leave stains on your jeans. Fill the washer's tub ahead of time, adding soap when it's halfway full. Add the jeans once the tub is completely full.
Wash in cold water
Cold water helps preserve the color. For best results, use a laundry detergent especially formulated for denim.
Air dry your jeans
Heat drying shrinks denim. It also adds more physical wear to the laundering process. As such, always dry jeans on a clothes line. If they are in direct sun, also keep the jeans turned inside out.
Heat dry only until they are damp
If it's necessary to use a machine dryer on your 501 jeans, only dry them until they are damp. Let them finish air drying in a warm spot.