Is the washer still completing the cycles ok?
Does the marks come off if you rub them or rewash them?
Also open the door and look at the door seal at the bottom were it attaches to the drum and peel it back a bit and see if theres all gunge or sludge in there and let me know.
Ok so is it taking the colour out of the clothes is that what its doing?
Does it do it to most items of clothes that go in or is it just the one item its done it too?
Ok what you can try is a service wash. Set the washer going on a 90 deg wash with no clothes in there and use a washing machine cleaner. Then run a wash cycle and this will clean the inside of the drum. As limescale and old degergent can build up in there and cause faults like this.
You may need to run a few as just one may not be good enough as if its built up in there it will take several cycles to clean this. As it all builds up in between the drums were you cannot see. So the cleaners can clear all that and hopefully stop marking the clothes as this is the most common cause of this kind of fault you have.#
So try that and see how it goes from there and that should cure it from there.
You have the Dr Beckman as thats good and some supermarkets do there own brands. Personally the Dr Beckam is the better cleaner so try that and see how it goes.
Your very welcome.