mix-blend-mode CSS property will decides how a text/ element should display on page depends on the parent elements background.
Email harvesting means fetching email addresses by crawling web pages using various scripts/softwares. These email addresses then used for sending bulk marketing emails or newsletters/spams. There are lots of softwares/bots available in the market which crawls the website and gives email address from its pages. These softwares are generally known as "Harvesting Bot".