the fact that i had to stitch this together cos lemmy doesn’t support multi image uploads probably doesn’t help but yea tumblr screenshots can be hard to parse if you’re not familiar with the format
tumblr chains work via reblogs, same logic as a quote retweet but the added text is below the original post rather than on top.
the purple on black text are screenshots of tags (they’re not always purple it depends on the theme of the screenshoter). tags are weird because they’re supposed to just be a way for people to mark posts, so for example you tag a post as “nature” and then people can search your blog for them or filter them out, but in time people started to speak in them presumably because they’re less invasive than adding text (tags aren’t carrier over by reblogs)