In 6.6 if I did
sage: matrix_plot(matrix([[1,2,3,4],[4,3,2,1]]))
I'd get a boring image (a bunch of squares)
In 6.7 I just get an axis.
This happens on my Mac OSX 10.10.3 and My linux machine (some recent Fedora). Both sages are built from source.
There do not seem to be any open trac tickets for this, but I may be doing something wrong. Am I?