What would have more impact on the visible coloring of a given K rated bulb, changing the bulb type or ballast? Correct me if I'm wrong, but I have been under the impression that the ballast itself can have as much impact on the coloring and performance of different bulbs as the bulb type itself.

Although I don't yet understand all the fancy electrical/chemical why's and such, one of these days I'll do the real research and figure all that stuff out...maybe.