artists_beware | Looking for advice -- pricing for being a colorist?

As the subject line says, I'm looking for some advice/input here.

I've been approached by a church friend of my uncle who is a professional artist to be a colorist for a children's book he has written and illustrated. He's seen my work and says my coloring skills are much stronger than his, and he likes what I do. The book is a personal project he's done on the side of his normal job which is in television production of some sort. He's planning on self-publishing this book and then going around to different schools in Texas to read, sign, and promote this book with the help of a publicist in Austin. He's sent me some sample pages from the book and the line work is solid -- he's definitely a good draftsman. I've spoken to him on the phone a couple times as well as exchanged a few e-mails, and he seems rather easy-going, sincere, and likable. He's also said that if we do end up working together on this I can feel free to use any of his marketing and industry contacts in the future to help get my freelancing business off the ground. This isn't one of those deals where he's wanting me to do it for free in exchange for exposure and contacts, etc., though; this is a legitimate payed job offer. He's just offering his contacts because I'm the niece of one of his close friends and he likes my work.

The thing I'm wondering about here is pricing. He's asked me to name a price for being the colorist, and I really have no idea what to ask for. I've only ever been approached as an illustrator, not a colorist, and my Graphic Artist's Guild handbook only has price listings for children's book illustrations. I don't know the length of the book yet, but I take it that it's a standard length. The illustrations aren't incredibly intricate, either. What kind of price is average for coloring? What kind of royalties would be negotiated? Does anyone here have any experience with being a colorist or dealing with colorists?

I've sent this same question out to all the other artists I know who are in the industry, and I figured