On 3 of mine I have first of all done STITD where the border joins the main body. (Know you're not "supposed" to do this, but start in the middle, but I had no problem doing it that way).
Then flipped over and quilted from the back side up - as they are wallhangings they were backed with natural muslin so much easier to get an even quilting pattern being able to see where I was going.
I've just quilted Candescence and although its a black background I did front front side up using a red. There are no rules, just whatever is the best and simplest way to do it.
I've done a 3-colour thread border treatment, I'm happy for the first go doing something like that - will post when I finish binding tomorrow.
I do think the OBWs are more challenging to quilt, because the eye is always drawn to the kaleidoscopes, and I try not to detract from them. Some of the illustrations in the books are incredible - they are so imaginatively and beautifully quilted.
I keep going back to just oogle them.