You need to be using around 300 to stop all of previous color from bleeding into the white color.
Of course the brand and type of filament will effect the purge volume settings.
You can expect to have larger purge blocks when you print with white.
I use a small 2 color rectangle model to test the purge volumes so I don't have us as much filament to test the purge volumes.
RE: Purge Volumes
You can also adjust purge volumes for individual colors. There's a button next to the infill area on the slicer (not in settings, on the plater screen) that says "Purge Volumes". Here you can adjust how much you purge for individual colors. This way when switching to black from orange, you don't need to purge as much, but when switching to white, you can purge more.