According to the text, discoloration of concrete can occur due to inconsistency in placement, exposure to the sun, and changes in aggregates. It is also affected by factors such as calcium chloride, water, installation methods, and the overall mix. While concrete starts out light grey, it can change color as it dries and improper sealing can lead to discoloration in the future. This can manifest as light or dark spots, color changes, or staining.