In the process of project iteration, you will inevitably need to go online. Going online means deploying or re-deploying; deploying means modifying; and modifying means risk.
Gray is between black and white. Grayscale release refers to a release process involving a smooth transition. Grayscale release can ensure overall system stability. You can find problems and make adjustments at the initial gray scale to minimize the degree of impact. What we often call AB testing or canary release are other forms of grayscale release.