Red Cabbage Indicator colour change with Sodium Metabisulphite

I made some pH indicator by boiling and straining cabbage juice and in an effort to keep it from spoiling for a while without having to store it at fridge temperatures I added some wine making stabiliser which consists primarily of Sodium Metabisulphite. I had previously tested some of it to check if adding it would affect the pH of the indicator since I wanted a pH neutral preservative. Well strangely after leaving it for a while I came back to find that the indicator had turned a weird shade of purple I had never seen the indicator take before. At the concentration it is at the original colour was a very dark purple - almost black. Now I know that the metabisulphite ion decomposes to produce SO2 gas which is acidic under aqueous conditions but I would expect that to change the indicator to its normal purple for a not very concentrated acid. But the colour it currently is is very pale and in fact when I pipette out some of the indicator it is almost totally clear. So I guess really my question is does Potassium Metabisulphite have some kind of bleaching effect I'm not aware of? 




<http://mylespower.co.uk/2012/04/06/homemade-ph-indicator/>
![enter image description here](https://i.stack.imgur.com/CRGFM.jpg)


Now we add the reducing agent (model compound).
![enter image description here](https://i.stack.imgur.com/swEt6.png)


That lessens conjugation and bleaches the anthocyanine. "*But the colour it currently is is very pale*" If the new compounds' residual optical absorbances are in the green, the solution will be iodine purple by transmission. 


 2