A super simple Tuesday tip to keep them looking bright and cheery, add a cup of white vinegar to the rinse cycle. Also use cold water to slow down the behavior of water, use liquid detergent as it is less likely to act with minerals, and wash the clothes inside out
How Vinegar Stops Colors From Fading
Vinegar can't stop the sun from fading colors, but it can stop the water and detergent from dulling bright colors. The dyes will not lift off the clothes and the clothes do not fade. Vinegar also dissolves minerals. If you have hard water that is combining with detergent and leaving a residue on the clothes, the vinegar will dissolve the minerals in the water.
Note: This tip works with all forms of colored clothes, not just colored jeans.