Sunburst isn't a morph, it's not even a definite coloration. Every one I've seen is completly different.
Do you know the "original" sunburst vieleds were simply just high orange? Now, people see one with a lot of yellow, and call it sunburst. In fact, my male has more orange on him when he's fired up than any other one I've ever seen. He's also got a ton of yellow too.
It's a marketing thing. That's it. Now, some breed for high yellow, high orange, blue, etc. It's just that - there's no huge genetic difference, locale, or even mutation.
now, those pied veileds someone's been selling fromg Germany... Those are a mutation.