Hi Lynn,
I offer Aqua Detox treatments (& have had training on the equipment) and I think it is important to say that the colour of the water does not determine anything. It can be light or dark, brown, green, orange, black etc etc depending upon 1.) the chemicals in the water to start with 2.) any chemicals already on the feet, for example from body lotions and 3.) chemicals secreted from the body via the pores of the feet during the treatment.
Sometimes the water can turn very dark (often a good sign of the cells releasing toxins effectively and therefore also a sign that they are absorbing nutrients effectively) and sometimes there can be hardly any colour change (I find this happens mostly when the chlorine content of the water is very high - you can smell it).
The important part of the treatment is not what is in the bowl afterwards but more the fact that a bio-energetic flow is created during the treatment which travels around the body stimulating cells, organs, micro-circulation and encouraging the clearing of any energy blockages in the bodies natural flow. Often people do not notice any difference in how they feel after only one treatment but after a course of treatments clients feel highly energised with a much calmer, clearer mind. It is excellent for restoring good sleep patterns, for easing joint pain, for clearing skin problems such as eczema etc etc.
I have found that this treatment is very commonly misunderstood as people tend to focus on the water at the end rather than how they are feeling afterwards. The flow encourages toxins to be released in the body and it is important to drink plenty of water during and after in order to flush these from the body.
I could ramble for hours but hope this info. helps you to uncover the 'mystery' of the colours.
J