As the season progressed and my birds got older the blue hue became less and less noticeable, especially on my lighter colored birds. My darker colored birds (Pearl Greys and Royal Purples) seemed to show it the most, so it may have something to do with the natural, wild charcoal grey/black base color gene, as well as maturity and possibly diet. Now, with Fall approaching and the breeding season coming to an end here, (and not much in the way of bugs and greens for them to forage while out free ranging this time of year) I don't see any blue faces or throats areas on any of my colors...
Maybe Casarius can answer this better if he happens to see this thread, he breeds some of the rare/wild varieties.