n.
a prepared mixture used to give gravy a brown colour.
The OED-3 includes citations from as early as 1769, and the term gravy browning is not restricted to Canada or even the UK (see Chart 1). The high frequency in New Zealand indicates that the term has been preserved in some Commonwealth countries. The BBC reference indicates that in Britain, it was "popular in the first half of the twentieth century, but is not widely used nowadays" and is becoming less widely available (see BBC reference).
See also COD-2, s.v. "browning", which is marked "Cdn & Brit", and OED-3, s.v. "browning" (n.2 2), W-3, s.v. "browning" (2).