Tom explains Mike originally contacted him about drawing the artwork as he was a big fan of Tom's comic Henry & Glenn. He also speaks quite a bit about his constant back and forth communication with the band, mostly Mike, approving designs, drawings, colors, and more.
Tom goes on to discuss his three different designs, two the band came up with and one he himself did - the one the band ended up choosing. He also mentions and shows the various color schemes that were considered, including a red-tinted version.
Tom's entire post is a really good read and gives a cool insight into the process behind the design and drawing of the album's cover. The post can be read over on Tom's website.
Thanks to desertrose for posting this on our forum