You could get a gray material for the cloak and say it's the "book version"...
Sheesh. So she's not just a stupid person who doesn't read, but she pays no attention to popular movies...
We may be going with gray anyway. But if it's not something pre-made, it ain't happening...
We're heading out to look again in a few minutes.
My daughter make a cloak at a Live Action Role Playing Props workshop a couple of years ago. I found some sort of thin faux suede that was a grey-green. It was great because it would 'change color' as it moved in the light. You'd even have time to make it because the cloaks don't take long at all, even if you put a hood on it. I've made one in an afternoon for one of my older sons.