Now, this is not about any type of taming or training technique and the study was not done with parrots (big surprise, right?) BUT it does go to their perception of us and what they pay attention to when deciding if we are trustworthy or not. Although there is anecdotical references from people saying that their parrot does not like them to wear this color or the other, painted nails versus no paint, long versus short hair, etc. I've never observed this behavior in any of the parrots under my care throughout the years. I've had hair of different length/colors/styles, different clothing, hats/no hats, etc (once I wore a broom tied to my back upside down, with the 'broomy' part sticking up from my head so as to deter a very aggressive macaw from attacking me and, another time, large beach towels tied around my waist going all the way down to the floor to deter a very aggressive eclectus from attacking my feet ) and no bird seemed to have any doubt whatsoever that it was still me. Having said that, I do believe that these are all things we should take into consideration when first dealing with a rehomed bird that is terrified of us because we remind them of a previous owner who might not have been the kindest to them.
https://gizmodo.com/birds-are-judging-y ... 1842699939