Colour Corrections and Fadage
The biggest change in modern salon hair colour besides added conditioning agents is the ability of the colour to open the cuticle very minimally in order to deposit the colour. This is important because a closed cuticle reflects more shine, will tangle less, and will protect the inner hair shaft from environmental damage.
The cuticle layer is also a key factor in colour fadage. Two things that will affect fadage are porosity (which is how open your cuticle sits) and colour selection (certain tones will fade faster ei. reds)