There are many possibel causes for a yellow tint following cleaning. Fortunately the same solution works for several different problems - get the fiber over to the acid side.
This can be accomplished by
1. An acid rinse
2. A neutralizing post spray such as Fab Set
3. Post spray with acid. Acetic acid / white vinegar (5% solution) will work but has odor. Citric acid (12 to 14 ounces per gallon) works without the odor but can leave a slight residue that will attract soil. A combination of Fab-Set (4 ounces), Citric acid (10 ounces) and a galon of warm water will not have the odor and will have less soil atracting residue than citric acid alone.
Rake in whatever you apply to help get it all the way to the bottom of each tuft.
Been there done that, Acid rinse works well. I typically use acid rinse with high PH products to prevent this correction. Only takes another few minutes and saves return trips and increases consumer satisfaction.