Here is a link to an interview with Mr. Duncan on BookSpot Beat
and the pertinent excerpt
"Jay Tomio - The cover to Escape From Hell is sweet as well. . .hell. Did you have any input or is that just Chris Roberson handling business?
Hal Duncan - Chris put the artist, Erik Gist, in touch with me, and we threw a couple of ideas back and forth based on the synopsis – because the novella wasn’t quite finished at that point. There’s a scene later on that we both thought would have looked really cool — you’d have had the heroes all standing there, tooled-up and facing out at the reader; it would have had a nice “bring it on, motherfuckers” vibe – but one feature would have been a bit of a spoiler. In the end we both preferred the option Erik ran with, which is taken straight from the prologue with just a tiny bit of artistic license used to bring Lady Justice into shot. If I remember right, Erik suggested it in a really early email, and described it almost exactly the way that I’d always visualised the scene. So I was totally over-the-moon that we were on the same wavelength.
Really my input came down to “yes, that sounds fucking awesome,” and “oh, but yeah, this Hell is cold and grey rather than fiery and red”. I mean, the traditional imagery of Hell-as-inferno _almost_ got in the way for a whole millisecond – most images of Hell are all black and red after all, thick crimson skies, darkness and flames – but Erik had actually picked up on the ashen wasteland feel I was going for, so it was just a matter of confirming that his first instinct was correct. The colour palette he used for it is perfect, I think, and I love the little touches of red on the key characters – Seven’s shades, Belle’s rosary and so on."