Oh! Thank you for informing me about the red book and the yellow bookshelf (that's actually not supposed to happen. I'll have to update that. Yikes.)
As for another angle, you're right. There is a another angle for this puzzle. Truthfully I hadn't thought it would be that difficult but well. I'm the one who made it and knows the answer already...
I will say that all the books do have a spot to be placed in, but not all of them have to go on a bookshelf.