There is nothing too special to consider before going to a salon for color correction. The most important thing is that you have a stylist who communicates well with you and is willing to learn what needs to be done for coloring your locks.
The most important factor will be rinsing, and you should request that they rinse your hair for a minimum of 10 minutes when removing any coloring products. Have them set a timer if necessary- otherwise coloring locks is pretty similar to coloring brushable hair.
Followers- any other tips?