How would you paint regret? The Nothing but Ghosts Giveaway

With Nothing but Ghosts, my third YA novel, set to launch in eight days (I think that's right), I thought I'd offer a signed copy to one of you who answers the following question: How would you paint regret?

It's a question that Katie's father asks her, as he restores an odd and ultimately revealing painting. A question that becomes integral to the mystery in which Katie is embroiled.

Here's the relevant scene from the novel. I'll have my son assist me in choosing one of your names (from a ha