14:12 Feb 4, 2011 

I don't really see the confusion - I think the term "très travaillée" means that the colour has to be thoroughly mixed before application. In don't see any indication that it should be mixed for a longer period of time than usual.

The 'très' in my opinion, simply means 'thoroughly' or 'well' in this case, and the "travaillée" rather than meaning 'prepared' means 'mixed', i.e. 'worked together' ...

13:40 Feb 4, 2011 

Hair colour always has to be mixed before application if one doesn't want streaks and burns. However, here you have "très travaillée en amont". So the "très" seems to have special significance, though you have omitted it from the term posted. I think it is about the pre-mixing time being longer than usual so that the colourant can be left on the hair for a shorter time than usual. I suspect that once it is well mixed, any further mixing makes no difference whatsoever, other than giving the hairdresser something to do to stop him/her becoming impatient and just slapping the stuff on early