Childrens (I think) book involving sheep named Blackberry and girl with silver hair

Sorry in advance for formatting, first-time poster on mobile. I remember reading this book when I was a kid, I think around 2010? Somewhere between 2008-2013. I know the main character was a boy, and he had a sheep he named Blackberry. There was also a girl (possible adopted sister? Not certain on how she knew him) who definitely had silver hair at some point in the book. The rest of these facts are a bit random and not as certain, but I remember Blackberry the sheep also turns silver at some point. There is a woman the boy lives with/visits that teaches him how to use plants to make natural dyes. I think aliens or something supernatural is involved and that's why the sheep changes colors? I've tried looking this book up a million times but I never turn anything up, and I feel like I'm crazy. I borrowed it from my elementary school's library and have no idea what the cover looked like or the names of characters. Please help!