You could try using 1 part Apple Cider Vinegar to 3 or 4 parts water as a final leave on rinse after you have rinsed off the shampoo.
LEARN A LESSON FROM YOUR DOG, NO MATTER WHAT LIFE BRINGS YOU, KICK SOME GRASS OVER THAT AND MOVE ON.
i also have a yellowing fur issue with sarah around her neck mostly. i am bathing her in duoxo ps shampoo for the yeast issues n kenic neem/oatmeal shampoo for the rest of her. i gotta say the kenic shampoo makes all my dogs white and soft. i also have to bath sarah once a week due to yeast issues but i have been going 2 weeks now since i changes her food slightly. i also see less yellow now to so im wondering if the yellow is not a allergy issue. my bostons also get a kinda dirty look to their white fur before i got them on the right food so maybe that is whats going on here to.