Don't judge your fertilizer effectiveness by color alone.
If the turf is dormant, or close to it, I would not expect to see any significant effects from fertilization. In short, timing is everything. If the turf is not actively growing (transpiring), then your fertilizer application is for the most part wasted, especially where leachable ions are concerned. If your not observing a visual change in growth rates due to the late season N application then you probably missed the boat, or something else is going on in the soil.
recommends September and October fertilizing. When in October depends on whether or not the turf is actively growing and can vary from year to year. Your best timed late season application will put on fertilizer at a time that allows the turf to utilize it just prior to going dormant, probably 1-3 weeks before dormancy depending on the type of fertilizer used.