A clear liquid like pure water can become coloured when it contains solids in suspension. this is due to the absorption and reflection of different frequencies of the visible spectrum.

Fine gold particles become red because they absorb the blue green part of the spectrum. This quality has been used in the glass industry for centuries to produce a red translucent glass known as cranberry or ruby glass. True colloidal gold is also red in colour. Colloidal silver is a medium to dark straw colour. Some manufacturers claim that the brown colour is due to some defect, this is completely untrue. This can only be attributed to a misunderstanding on their part of basic chemistry. The brown colour is due to very small particles, large particles produce a weaker colour and ionic solutions have no colour at all, because they do not contain any particles.