Hi again Rob
The simple fact is you can't tell whether Direct dyes have been used unless you carry out the correct laboratory tests...these will be way outside the capabilities of most cleaning technicians.... including me
With colour changes caused by a chemical reaction they can often be reversed by using a corresponding opposite pH chemical
i.e. if it is an alkaline reaction from a chemical with a pH of 9 then you will neutralise it by using an acidic solution to the value of pH 5 (both 9 and 5 are two digits away from the neutral 7 on either side of the pH scale)
Derek