What are the three DELTA (Δ) values and how do they relate to fading?

These values relate to the noticeable color change from fading. A color difference fading of 1 DELTA (Δ) is noticeable to the average person’s eye, 2 DELTA (Δ) becomes more apparent, and a color difference fading of 3 DELTA (Δ) is very evident to most people.