What to consider when repainting fork from black to white
I hope there is some kind of industry standard when it comes to the color.


Surly offers such a service for its bikes:


  RAL is a color code number system used by paint manufacturers. 


Not so sure about other vendors.


  Do I need to remove the black paint first or can I just color over that?


You do not need to remove existing paint. However, it is recommended to use a primer before applying new color layers, and also a clear coat on top of that.

I used spray rattle cans (primer, color and clear coat) to repaint a suspension fork on one of my bikes. Not the best tool for a fine paint job, and even that required a couple of attempts to gain the experience to do it right. However, I am satisfied with the result, given that the fork is on a beater bike.

Good advices on hand repainting of bicycles can be found here. There are other good web resources that I used to learn about the process. Or, you can leave it to professionals — there certainly are services for quality paint jobs.