And not all manga is in black and white. I'm not sure what your point is. There are plenty of novel-sized books in various genres which use colour. And, as someone who sells ereaders every day at work, I can definitely say that there are some people out there who are disappointed that they can't see book covers in colour, let alone maps, illustrations, colour-coded diagrams and photographs.

I'm with pdurrant on wanting a robust, higher res display first. I'm just saying that 6" screens are useful for more than just novels. It's like saying that normal paperback books are mostly fiction - you're forgetting about the wealth of non-fiction books available in that sort of form factor, both in physical and electronic editions. There is a huge range of scientific and technical ebooks out there, and a great many of them use photographs or colour-coded diagrams.

e: Come to think of it, even fiction uses maps and illustrations - take fantasy or children's novels, for instance. Not always in colour, but I suspect that's more because printing the pbooks completely in black and white would be cheaper, something which isn't really an issue with ebooks, so something which might change over time as ebooks become more the norm.