Help needed with discoloured white Egyptian cotton duvet cover.?

I bought a fantastic Egyptian cotton duvet cover and a pair of pillow cases; they are luxuriously soft and a dream to sleep with.

For sometime now I have noticed the top of the cover has become noticeably discoloured. At first I thought it was the direct sunlight, I was correctly informed that the sun bleaches, so this would not be the culprit.

I wash it regularly with biological soap tablets and a 1/4 cup of white vinegar in place of fabric softener. I have a very good front loading washing machine too. I follow the care labels correctly also.

It could well be that it is just dirty, as it is the top of the duvet cover. I was hoping some one could give some ideas as to why it has changed colour, is it just a build up of dirt and if so why has it not been washed out?

The care label has the no bleach symbol, but does any one advise me to bleach and would it solve the problem? I thought this was the most likely solution.

I know there are many stain removing products on the market, but I am not sure comfortable I am with them. I don’t leave stains and wash to make sure things stay clean in the first place.

Kindest regards,
claughton86

Here are some photos of my duvet cover:

http://www.flickr.com/photos/26655062@N05/2765382330/

http://www.flickr.com/photos/26655062@N05/2765377944/

Try using Napisan, you can use it in the washing machine. I think you may be better off when you have it bright again to wash it more often. I say this because I used to have a white bed valance and as they don’t get washed so often as sheets etc. I noticed that the skirt bit was a noticeable yellowy colour compared with the centre (that was under the mattress). White, surprising, goes a bad colour from being exposed to the air. Weird I know but true.