Visually it should be quite easy: colloid silver is represented by a yellow-to-brown colour, where the hue depends on concentration of silver and the particle size (or the age of the product respectively).

Should colloidal silver be clear or brown?

In the case of silver supplements… Smaller is Actually Better – which means that colorless is better! Colloidal Silver is typically a suspension containing neutral (larger) silver particles, which give it a yellow or amber hue.

How can you tell if colloidal silver has gone bad?

A bottle of colloidal silver should be dark blue-gray, as light reflects off the particles. If it goes clear and the silver has changed or dropped to the bottom, it's no longer a colloid!