Looks to be more of a genetic thing then a problem. What week of flower are you in with these?
Looks like more genetics to me as imsickkid said. all i really see is some white spots like maybe hard water being used in a humidifier but there are many knowlegable ones here to help. you can always fill this support ticket out. Plant look good
What strain, Seed bank, or bag seed
Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
Vessels: Pots, Grow beds, Buckets, Troths
PH of Water, Solution, runoff (if Applicable)
PPM/TDS or EC of nutrient solution if applicable
Indoor or Outdoor
Temps; Day, Night
Humidity; Day, Night
Ventilation system; Yes, No, Size
AC, Humidifier, De-humidifier,
Co2; Yes, No
Week 5 is a bit early for so much fade, looks like it ran out of nitrogen, what are you feeding them?