Someone I talk to here at work mentioned that on the tv, Gretchen, Elliot, or Rose mention the Blue Meth still being around. They think THAT is what Walt was reacting to, not what they were saying about Gray Matter.
Almost like they slipped in the blue mention real quick, then changed the subject and distracted us.
He may not even do a thing towards Gray outside of maybe his "showdown" hitting the news and he embarrasses them again after they claimed he was no longer around.
I mean - I think it has to be everything hitting him at once. His family rejected him and wouldn't accept his money. His signature blue meth was still in circulation even though he's been out of the game for a year. AND Gray Matter just claimed that his only contribution to the company was coming up with the name. He realized he wasn't giving his family anything and he wasn't going to be remembered or more importantly, respected by anyone. Basically, his sacrifice and hard work was for nothing.