My cream colour hand towels have quite large grubby areas in the part of the towel that is used to dry hands.
My suspicion is that it is excess hand soap as my daughter (has SEN) will often use too much soap and then dry her hands without rinsing them properly. I'm loathe to pick her up on this too much as sometimes she doesn't wash her hands under the tap at all...
I always wash at 60 or 95 degrees using bio powder, no fabric softener. Today I washed them in vinegar, then bicarb of soda. They still look grubby!!
Before anyone comments - cream colour towels pre-date my daughter if anyone wonders why we have an impractical colour
. Still plenty of life left in them, if only I could get them looking clean.