SunilSirdesai: Liquid will yellow when residual acidic impurities in the liquid are exposed to air or light. The amount of impurities present determines the rate of the yellowing. This means the rate of yellowing will vary from batch to batch and from monomer to monomer. There is very little the nail technician can do to prevent yellowing under these circumstances. Not exposing the liquid needlessly to light or air helps only minimally.
DougSchoon: Enhancement yellowing is usually a sign of either contamination or service breakdown. Contaminated liquid monomer, brushes, containers or dappen dishes are often the causes.
Some products become damaged when exposed to UV tanning beds or sunlight.