I know your question isn't directed at me, but just want to say I'm not sure why I overlooked the obvious point you just made lol (semi washes out).
Just based on my own experience w/semi though: I used semi-perm. dye for years (recently exchanged it for henna/amla treatments), and that semi-perm. color built up in my hair after repeated applications and became permanent. Of course if this is one of the first applications for the OP, you're right ... why not just keep rinsing it until it washes out?
Last edited by Korkscrew; 01-09-2013 at 06:16 AM.