The colour almost made it look like ice at first glance! :)
You are definitely right! It is light gray rock with a curious blue cast to it. Very noticeable when you are there.
To make the photo come out right, I did some serious masking on the terrain outside of the great gully. Basically needed to bring that exposure down and lift up the exposure in the gully. There is a chance that my manipulations make it even a bit more blue than it is in real life. But in general...the rock does look blue :-).