Really early on, with the original castle sets, where all the wall pieces were yellow. I believe the space sets were the first grey bricks.

The LEGO group has always been protective of their brand and nervous about being associated with potentially violent content, turning down a partnership with the Halo games because of that. For years, they didn’t want to make grey bricks because they were afraid kids would use them to build tanks. All this to say, this seems pretty on brand for the LEGO group.

Did not know this fork exists. Thank you for enlightening my day, Internet stranger.