Silver colloids have a color based on their particle size, ranging from orange to brown to yellow to clear as their size decreases. The property is called Surface Plasmon Resonance. Particles smaller than 5 nm are “subplasmonic” meaning they are clear and colorless solutions. Argentyn 23 Bio-Active Silver Hydrosol is a mixture of positively charged silver ions and silver nanoclusters with particles as small as 0.8 nm (nanometers). Color is visible when particles are larger (above 5 nm). A larger quantity of particles can also lead to visible yellow color as more particles absorb more light. Darker color is an indication of one or more of the following: even larger particles, compounds (salts or proteins), reduction of bio-active silver ions, or impurities. A smaller particle size is desirable due to greater surface area available for conversion to bio-active silver. Since visible color is an indication of larger particles, then visible color is your visual cue to less effective silver products.