Subject: What is the species that causes the yellow color of vitamin C solutions on

Fresh solutions of vitamin C (ascorbic acid) are colorless. After a few days 
these solutions turn bright yellow; after weeks dark yellow. What molecule is 
formed? (and turns your urine also yellow?). The only thing I can come up with 
is a reaction with dissolved oxygen (reduction of ascorbic acid) to 
dehydroascorbate. (Oxygen in acidic solution is quite a strong oxidator) Yet: 
if I add a strong 30% hydrogen-peroxide solution (a very strong oxidator)to a 
fresh C-solution nothing happens.
One would expect the solution to turn yellow immediately.
Is there a chemist out there who can help?

Re: What is the species that causes the yellow color of vitamin C solutions on