The reason the area has turned to light brown almost green is because the dogs urine has already caused it to bleach out. Permanent damage has already been done, the discoloration is not going to go away. Your only solution would be to dye the lightened areas to try to match the rest of the carpet.. I'd done so using tea or coffee as my source of dye because you can vary the shade by adding water. I start with what I think looks close and can then darken as needed. Sorry I don't have better news for you. Good luck.
Do a search on Thriftyfun for the "pee recipe" which I posted a while back. Test an inconspicuous area first.
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