Reposting Aubreygraces pedigree
It does indeed indicate dom to Grey Matter but unfortunately we can't know from what we see that the Grey Matter is pure, its the result of a double hidden pull and we can't know both its parents hid Grey Matter.
The best way to confirm will be to pull the Grey Matter using a more recessive eye. Unless you have proof both the Greys parents did indeed hide it. Maybe if you shared the pedigree for the Grey Matter Ivy or I can take a look and see for you