Pictures have surfaces from the first sea trial that maybe show a blue hull. Now there has not been an official word from the yard, RCL, employees, etc. about this yet and it could be a primer, coating, etc. but these photos are strong proof that a blue hull might be in the works.
Also, there are other explanations of the blue. The pictures do look like the hue and saturation have been tweaked a little, or it could be a reflection.
See for yourself and come up with your own determination.
(Photos courtesy of Folke Österman via Shipspotting.com)