The first thing to do is find the culprit and pull it out. Then rewash all the clothes using a nonchlorine bleach or a cup of white distilled vinegar in addition to your regular laundry detergent. Do this BEFORE you put the clothes in the dryer.
If you have already dried the clothing or the dye transfer is heavy, you will need to take time to soak the clothing before rewashing. Mix a solution of oxygen-based bleach (Clorox 2, OxiClean or Tide Stain Release) and warm water following the package directions. Submerge the stained items and allow them to soak for 24 hours. Check the clothes and if the dye stains are gone, wash as usual. If they remain, soak for another 24 hours with a fresh solution and then wash.
This is why clothes should be sorted. Just because something hasn’t faded before doesn’t mean it never will. Sometimes it takes several washings before dyes begin to wash out and cling to the unsuspecting!
Specific questions? Just ask here.