How would you get out rose pink staining from white socks?

I think it's being caused from saliva - they have kongs (black) stuffed with tinned butchers tripe.
Over the last week I've noticed that she's got rosey pink staining on her white socks.
I've tried the no-rinse purple stuff and it's taken some of it down but I still notice it.

Is there anything that I can do to rid the white socks of this staining?

There is a special whitening shampoo available, it is blue in colour in the bottle and has the same effect that ultra violet light has on whites. I am sorry I cannot remember the name of it, but if you ask around in the Boxer world several people use it. you can just put a small amount on a damp cloth and wipe the exact area, you will see results immediately, just like magic!