I just got a fab book , its from an american guy and i saw his website and thought it would be a rip off as theres like 5 books on different aspects ..they are $59 each but you can download the ibook straight away instead of having it shipped which is what i did its called "how haircolor really works " by david valesco .. Its gives you more insight into how porosity affects color etc.. This guy was the head trainer for wella for 10 yrs so he knows his stuff , but he doesnt talk products .. He gives good examples and explanations on how to formulate for the client etc.. I know for me i am glad i bought it as theres not many books that give you that bit more extra info .. I will be getting the rest of them ,hope this helps