I know it's only a model either way, but the grey ties just look more realistic to my eyes. The blue ties look like toys- looks like they were made of plastic. And the idea that the Empire would paint their fighters blue just seems goofy and out of place.
But I do understand the want/need to have them stand out against the Stardestroyers/DS... Didn't Ady say that they would be less blue than the DVD/BD but more so than the ANH:R ties? ...They still look awfully blue in the latest clip.