The grey part you are referring to is still terra cotta tile. It is indeed a different shade than what's on the interior swoopy bits, but just as nice and has the shame shimmering properties that change color depending on the light.
Definitely not cheap nor concrete. Obviously taste is subjective, but I think they both look great.
National Music Centre by
Construction Mania, on Flickr
Where they cut some costs is the east side of the building, as the assumption is something will be built next to it at some point.
National Music Centre by
Construction Mania, on Flickr