I found an essay written by Rothko. The page initially starts out as a biography but the essay is there. I haven't highlighted it yet, so have at it your own way.
Dore Ashton became something of an expert on Rothko after his Pratt lecture. After reading the article I was convinced I could find the lecture somewhere. I found a couple of books which indeed had a transcript, but I had to buy them. I did some more searching and I found a book whose preview had [almost] all of the Pratt lecture. I found it! These are (mostly) Rothko's own words about his own painting. There are even some questions from students! The lecture doesn't start until page 125 but the bookmark takes you to a search result already. Just click the link that reads page 125. This is the beginning of the speech Mark Rothko gave at Pratt institute. The screen shot function is a lot messier than diigo and so if anyone has any tips on how to use diggo without needing to take a screenshot I'd really appreciate it.