Ron Barbagallo of Animation Art Conservation has an extensive interview with Ralph Eggleston, one of Pixar's leading production designers (The Incredibles, Finding Nemo), about his work on Wall-E.
I don't think I have ever read a more detailed interview about the visual development of a Pixar movie. Ron asks all the right questions making this a must-read for anyone interested in color design.
Just in case you haven't listened to it already, creative screenwriting magazine offers a Q&A with Andrew Stanton focusing on his work as a screenwriter on Wall-E. He also explains about the origins of Finding Nemo and how he got into Pixar. At 71 minutes length, it is one Jeff Goldsmith's longer podcasts.