Why is my washing machine door seal black?

Generally this is due to low temperature washes, typically 20° or 30°.
We are all doing our bit for the enviroment & aiding our pockets by doing low temperature washes however, the downfall is bacteria builds up inside your drum at low temperaure.
After several months of low temperature washes bacteria built up hidden inside the machine drum then spreads to your door seal & detergent drawer.
As a service engineer customers would ask for a replacement door seal however this is only a short term fix without removing the bacteria hidden in the machine tub.
Using Washer Wizard twice annually will clear hidden bacteria harboured within the drum & clear mould and mildew from your door seal.

How can I clean my mouldy washing machine door seal?

By now you have probably realised no matter how hard you scrub the stubborn mould & mildew remains.
The simple solution would be to use the Washing Wizards potion.
Other options are available however without cleaning the hidden part of the drum mould & mildew will return in no time. They are also far less affective & can take a considerable amount of effort.

This video should be helpful in cleaning severe cases of mould & mildew on your door seal.

Try to do regular hot washes, whites are ideal for this & can be washed upto 90° - Check labels for suitability
A simple wipe of the machines rubber door seal after the days laundry is complete will reduce the chance of mould, mildew & bacteria build up.
Leaving the door ajar can also help