Ian Clark should mind his own business.
Since he's the goalie coach for the team, what his goalies wear is his business.
Now why he believes this leads to improved performance and if that rationale actually is backed up by data, who knows.
There are lots of people that believe that white goalie pads and gloves make it harder on shooters. Just as some shooters think that black tape makes it harder for goalies to pick up the puck.
I doubt that these theories will ever really have solid data to back them up or refute them.