I have very little to add about the color aspect, but I can say that I love my Kobo. I've had three Kindles before buying the Kobo, which I got because it has a "better" integration with my local library (better in quotes, because I still have to do with the Adobe DRM, which is so bad on Linux that I borrow my wife's computer just to transfer). The Pocket integration is fantastic, as are the physical page turn button…
In my experience koreader integrates much better with calibre and allows managing my library with a filestructure. So that is a requirement for me.
Also the stock firmware on the Pocketbook was able to deal with my huge epub archive, because it didn't require indexing the library on the device, which Kobo struggled with.
From that experience I would pick a Pocketbook over a Kobo.
But maybe I should give Kobo another look.