Possibly meant in the sense of Blue Tribe / Red Tribe from here: https://slatestarcodex.com/2014/09/30/i-can-tolerate-anythin...
But maybe it's just more generally red as euphemism for conservative (b/c of how political maps are coloured in the US).
But maybe it's just more generally red as euphemism for conservative (b/c of how political maps are coloured in the US).