yellowing

/Y EH1 L OW0 IH0 NG/
verb
  1. 1

    To become yellow or more yellow.

  2. 2

    To make (something) yellow or more yellow.

noun
  1. 1

    The process of turning yellow.

Source: https://en.wiktionary.org/wiki/yellow, https://en.wiktionary.org/wiki/yellowing