There are additional considerations when coloring hair. That includes the texture, this is the degree of coarseness or fineness of the hair shaft. This is important because coarse hair can tend to be resistant, while fine hair may be not so resistant.
Also, porosity, this is the hairs ability to absorb moisture, liquid or chemicals. This is the main factor when deciding product, formulation, and appropriate technique and processing time. Some things that may affect porosity include but are not limited to sun exposure, chemical products such as hair color, even some shampoos. Even heat from hair dryers or straighteners can effect porosity.