The pink paper is a customization of the white paper to match the DeFiChain color, pink. It is "essentially a live paper, subject to constant change as specifications are added, that will set the overall direction of DeFiChain for the next year [Part I was written on 13 April 2021] and beyond," according to the description in the blog.
This is the original on Github.
This is the blog entry for Part I, on defichain.com.
This is the blog entry for Part II, on defichain.com.