What part of the hair structure does it affect for quasi colours?

Quasi-colors primarily affect the hair's cuticle and cortex. The cuticle, which is the outermost layer of the hair, is where the color molecules enter and deposit, while the cortex, the inner layer, contains the natural pigment (melanin). Quasi-colors typically coat the hair and can penetrate the cuticle to some extent, allowing for a semi-permanent change in color without fully altering the natural pigment. This results in a temporary color effect that can fade over time with washing.