The guys who do mine are very good and reasonable at it. One guy boils the skull until all the skin and external flesh, etc... is off. Then he takes the skull and power washes the brains out and gets he skull absolutely clean. Then if it hasn't stained brown he'll bleach it with a tooth brush and let it sit in the sun... he'll repeat this 2 or 3 times. If it does have browning on it, he'll paint it with high gloss white paint which really makes the skull pop. He's in the process of getting mine done- when he's done I'll post some pics of how it turns out. I know most guys want to do this themselves and they take pride in doing their own-- but I don't have a power washer nor do I have anything capable of boiling an entire skull. Plus I get the "buddy" discount from him which makes it a no-brainer. Good luck with yours and if you have any questions I can relay them to him.
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!