It’s a sad fact, all clothes will fade over time and there’s nothing you can do. 
On a more positive note, you can slow down or stall the inevitable, with some pretty easy tricks. 
  1. Turn your darks inside out. When the clothes rub up against each other, they damage the outer fibres containing the dye, which releases the dye. The nice thing about this is turning you clothes inside-out actually takes LESS effort when getting undressed, just rip them off your bod like you’re still 5. 

  2. Look for detergents without optical brighteners and bleaches. Both are good for keeping whites white, but no so good for keeping darks dark. Most detergents that are biodegradable, like Dirt, don’t contain bleaches or brighteners.

  3. Wash clothes less. An easy win. Some experts suggest leave months, not weeks between washes for jeans.

  4. Keep the heat to a minimum. Wash as cold as you can, and don’t tumble try for longer than it takes clothes to dry. The more heat + time in the dryer, the more fiction and fibre damage and, as per point 1, the less dye remaining. 

  5. Keep your clothes inside out if you are drying them in the sun. The sun acts as a natural bleach which will fade your clothes nice and fast. 
In summary, wash less and undress like a child and you'll have the freshest clothes in town. 
Frankie Layton